Friday
September 4, 2015

Posts by Reiny


Total # Posts: 30,724

math
I am not even going to guess what that means.
February 8, 2015

maths please help and explain
Did you not look at my reply to this from yesterday morning ? http://www.jiskha.com/display.cgi?id=1423307265 You have typed it exactly the same way, the same lack of brackets in the numerators, and the same ambiguity in B.
February 8, 2015

trigo
your equations all fit the pattern y = a (sin or cos)(kx) where |a| is the amplitude and the period is 2π/k I will do one of them , you do the others in the same way. 2. y = 4sin(5x) amplitude is 4 period = 2π/5 radians dy/dx = 4cos(5x) (5) = 20 cos(5x) = 0 for any ...
February 8, 2015

math
calls received after one session of calls = 4 calls received after two sessions of calls = 4^2 = 16 calls received after three sessions of calls = 4^3 = 64 ....... calls received after n sessions of calls = 4^n Please finish the question
February 8, 2015

math:order of operation
Pattern: at start: 3 butterflies after one minute: 3(2) = 6 butterflies after two minutes: 3(2)(2) = 3(2^2) butterflies after three minutes : 3(2^3) butterflies after four minutes : 3(2^4) butterflies but at that point she captured 7 of them after 4 min, number on screen = 3(2...
February 8, 2015

PreCalculus
I will assume the chips are not returned after being selected. a) You want the situation GGGGN and its other 4 variations, where N stands for non-green Prob(GGGGN) = (30/60)(29/59)(28/58)(27/57)(30/56) = 135/4484 But there are C(5,4) of these Prob(exactly 4 green) = 5(135/4484...
February 7, 2015

dot product of vecotrs
Sure looks like you corrected the typo, but made no effort to adjust the corresponding arithmetic. http://www.jiskha.com/display.cgi?id=1423332996 The unnecessary duplication of work could have been avoided.
February 7, 2015

Math Help
You need brackets: (1+ sec u)/tan u - tan u/(1+sec u) I am going to guess that you have just learned: sin^2 x + cos^2 x = 1 and its variations ... tan^2 x + 1 = sec^2 x cot^2 x + 1 = csc^2 x So (1+ sec u)/tan u - tan u/(1+sec u) = ( (1+secu)^2 - tan^2 u)/(tanu(1+secu)) = (1 + ...
February 7, 2015

Math
since sinx = -12/13, and tanx is positive, x must be in quad III in your triangle: sinx = -12/13 ----> the given cosx = -5/13 tanx = -12/-5 = 2.4
February 7, 2015

geometry
one circumference = 8π ft 3 miles = 3(5280) ft or 15840 ft number of rotations = 15840/8π) = appr 630 times
February 7, 2015

Math
NOT to be a trig identity requires a single exception so take an angle for which you know the trig rations and test the equations e.g. let x = 45° you know sin^2 45 = cos^2 45 = 1/2 tan^2 45 = 1 and cot^2 45= 1 also sec^2 45 = 2, and csc^2 45 = 2 What do you think?
February 7, 2015

^Math.^ Pls,I need help
LS = (a-b)^2 = a^2 - 2ab + b^2 RS = (a+b)^2 - 4ab = a^2 + 2ab + b^2 - 4ab = a^2 - 2ab + b^2 = LS Q.E.D. or (quid est demonstrata) (Thus it has been proven)
February 7, 2015

Vectors and Math
I will use the notation: a = -i-3j+k = <-1,-3,1> b = 2i+4j-5k = <2,4,-5> and (3a+4b)(2b+4a) is the dot product = ( <-3,-9,3> + <8,16,-20>) dot (<4,8,-10> + <-4,-12,4>) = <5,7,-17> dot <0,-4,-6> = 0 -28 + 102 = 74 check my ...
February 7, 2015

maths please help
You will need brackets in the numerator as well in A B appears to have a typo C) notice the middle term denominator factors and it becomes the LCD 3/(x-3) - x^2/((3-x)(2+x)) - 2/(x+2) Do the others in the same way hint for D after you insert the brackets in the top you get (x+...
February 7, 2015

Math
I will assume you meant the numerator to be ( √(x^2+25) - 13 ) , so lim ( √(x^2+25) - 13 )/(x+12) , as x-->-12 = lim ( √(x^2+25) - 13 )/(x+12) * ( √(x^2+25) + 13 )/( √(x^2+25) + 13 ) = lim( x^2 + 25 - 169)/( ( √(x^2+25) + 13 )(x-12) ) = ...
February 7, 2015

math
volume of cone= (1/3)π(49)(18) = 294π cm^3 Height needed in the cylinder to hold that volume π(14^2)(h) = 294π h = 276/196 = 3/2 or 1.5 cm
February 7, 2015

math
ignore my reply above,
February 7, 2015

math
Adjust this solution to fit your problems, they are the "same" http://www.jiskha.com/display.cgi?id=1423275251
February 7, 2015

math
15^10/15^9 = 15
February 7, 2015

math
factor pairs of 36: 1 36 2 18 3 12 4 9 ---- so I could draw 4 different rectangles of area 36 with whole number sides factor pairs of 15 1 15 3 5 ---> only 2 possible
February 7, 2015

math
number of large --- x number of medium -- y number of small --- 180-x-y 6x + 5y + 4(180-x-y) = 820 6x+5y+720-4x-4y=820 2x+y=100 or y = 100-2x 22x+14y+11(180-x-y) = 2380 11x + 3y = 400 sub in y = 100-2x 11x + 3(100-2x) = 400 5x = 100 x=20 then y = 60 So 20 large, 60 medium and ...
February 7, 2015

pre cal
y' is a common factor y' (6y^2 - x) = x+y y' = (x+y)/(6y^2 - x)
February 6, 2015

Calc
Thanks Steve, I see it now, used 2x^2 instead of 3x^2
February 6, 2015

Calc
how about let u = 2x-3 then 2x = u + 3 x = (u+3)/2 then y = 2(u+3)^2 /4 - 2 = (1/2)(u^2 + 6y + 9) - 2 dy/du = (1/2)(2u + 6) = u + 3 = (2x-3) + 3 = 2x dy/d(2x-3) = 2x
February 6, 2015

Math
Label the top of the pole as T and its base as O in triangle OTP, tan38 = 15/OP OP = 15/tan 38 in triangle TOP, cos 25 + 15/OQ OQ = 15/tan25 in the right-angled triangle POQ PQ^2 = OP^2 + OQ^2 I will let you finish it.
February 6, 2015

aalgebra
the solution will be a point of the form (x,y)
February 6, 2015

math
A^2 = 9 8 16 17 which is A+B so B = 8 6 12 14
February 6, 2015

spinner
think of it as A, B, C AB AC BC mathematically: 3 choose 2 = C(3,2) = 3!/(2!1!) = 3
February 6, 2015

Math
1/5(2x-10) + 4x = -3(1/5x + 4 I see no closing bracket on the Right Side so I will assume you meant 1/5(2x-10) + 4x = -3(1/5x + 4) (1/5)(2x-10) + 4x = (-3/5)x - 12 multiply each term by 5 2x-10 + 20x = -3x - 60 25x = -50 x = -2
February 6, 2015

Math
Steve did this for you http://www.jiskha.com/display.cgi?id=1423099260 always check back before reposting
February 4, 2015

Math
Most mathematical authorities define an exponential function as f(x) = a^x, where a is any positive number, a ≠ 1, and x is any real number so #1 is True #2, what about y = (1/2)^x as x increases, y decreases, so False
February 4, 2015

Math
since all 3 factors have an exponent of 1/4 you can say: ⁴√18× ⁴√9 ÷ ⁴√2 = (18x9÷2)^(1/4) = 81^(1/4) = 3 (one of the basic exponent rules: (a^n)(b^n) = (ab)^n
February 4, 2015

Calculus 2
equating coefficients = partial fractions ? let (x^3+5x^2+12)/((x^2)(x^2+4)) = A/x^2 + (Bx+C)/(x^2+) = (Ax^2 + 4A + Bx^3 + Cx^2)/(x^2(x^2+4)) = (Bx^3 + (A+C)x^2 + 4A)/(x^2(x^2+4)) so B=1 A+C=5 4A=12 ---> A = 3 in A+C=5 ---> C=2 so we can write: (x^3+5x^2+12)/((x^2)(x^2+4...
February 4, 2015

7th grade math
good job checking your answer: n is at most 6, so 6 + 7 ≤ 13 ??, YES
February 4, 2015

geometry
The surface area of the side of a cylinder is 2πrh, in effect, the circumference of the circle times the height. (Visualize taking a piece of paper and forming it into a cylinder.) So for yours, the radius is 7 cm surface area = 2π(7)(45) = appr 1979 cm^2
February 4, 2015

Math
Do you just want the inequation?, if so, then 4n - 6 < .5(-n) If you want a solution: each term multiplied by +2 8n - 12 < -n 9n < 12 n < 12/9 n < 4/3
February 4, 2015

Math
write it this way: (a-7)/10 = (a-2)/8 cross-multiply 10a - 20 = 8a - 56 2a = -36 a = -18
February 4, 2015

math
If you know your trig relations and formulas, then its clearly C otherwise, you could test them with some angles. Remember, if you find even one exception to a mathematical rule, then that rule is invalid A, let Ø = 20, then its complement is 70° sin20 = appr .342 ...
February 4, 2015

math
radius of each balloon = 7.2 inches Volume of each balloon = (4/3)πr^3 = (4/3)π(7.2)^3 = appr 1563 cubic inches
February 4, 2015

Algebra
number of nickels --- n number of dimes ---- d n+d = 40 5n + 10d = 285 divide by 5 n + 2d = 57 subtract the two equations: d= 17 then in n+d = 40 n+17 = 40 n = 23
February 4, 2015

Math
Your description is not clear. A square prism has two ends that are squares, basically a box. see: https://www.google.ca/search?q=square+prism&biw=1663&bih=929&tbm=isch&imgil=Rh18AWgVlirFIM%253A%253BaxhcbOt3GqfHpM%253Bhttp%25253A%25252F%25252Fwww.k6-geometric-shapes.com%...
February 4, 2015

math
adults -- x kids --- 300-x solve: 15x + 12(300-x) = 4140
February 4, 2015

algebra 1
divide the 2nd by 3 ---> y = -5x + 2 first equation: y = -5x + 15 Since the two lines are parallel, there will be no solution, since they will never intersect.
February 4, 2015

math
first line: slope = (7-1)/(7-1) = 1 y = 1x + b using either point, I will use the simpler (1,1) 1 = 1 + b b = 0 first equation: y = x 2nd line: follow my steps.... to solve, sub in y = x from the 1st into the 2nd
February 4, 2015

Algebra
amount of $9.00 nuts --- x lbs 9x + 5(50) = 6.5(50+x) 9x + 250 = 325 + 6x 3x = 75 x = 25 your conclusion is .... ?
February 4, 2015

Algebra
prob(of your event) = (4/52)(3/51) = ...
February 4, 2015

Trigonometry
done look at your post which you had 6 minutes before this one
February 4, 2015

Trigonometry
label the top of the building as P and its bottom as Q look at triangle PAB angle A = 21° angle ABP = 180-32 = 148° , then angle APB = 11° using the sine law you can find PB then in the right-angled triangle PBQ BQ/BP = cos32 BQ = BPcos32 = .... add 100 and BQ
February 4, 2015

maths
Well, here I am, thinking all my life that a quadrilateral had 4 sides.
February 4, 2015

Algebra 1B
This topic usually requires several days in a standard classroom situation, so it is not possible to answer in a single post of this kind. I just Googles, "factoring trinomias" and got oodles of websites. I have been a fan of Khan Academy for years and this one ...
February 4, 2015

Algebra 1B
I suggest grouping 3y^3-9y^2+4y-12 = 3y^2(y - 3) + 4(y - 3) = (y-3)(3y^2 + 4) For factoring questions like this, you can always check your answer by expanding it, to make sure the original comes back
February 4, 2015

Algebra 1B
For the coefficients, the GCF is 6 for the variable it is x^3 so 6x^3
February 4, 2015

Algebra
ages now: Amy --- x Rosa --- x+14 Three years ago: Amy --- x-3 rosa ---- x+11 x+11 = 3(x-3) x+11 = 3x - 9 2x = 20 x = 10 sub into my definitions
February 4, 2015

algebra
Jamar: w = 3m+ 14 Scott: w = 5m + 8 A rather silly question!
February 4, 2015

calculus
Make your diagram using an x-y grid at noon, place ship B at the origin, and A on the left side of the x-axis After some time of t hrs, let B's position on the y-axis be Q, mark BQ=25t draw a vertical line in the South direction and label A's position as P, marking AP=...
February 4, 2015

Geometry
simplest way, list the points counterclock-wise, repeating the first point you started with 5 5 3 4 8 3 5 5 area = (1/2)(sum of down-products - sum of up-products) = (1/2)(20+9+40 - (15+32+15)) = (1/2)(7) = 7/2 , just as Steve had btw, this method works for any convex polygon
February 3, 2015

Geometry
There are many ways to do this, you will have to tell me at what level of math this is. e.g. Have you heard of Heron's Formula? e.g. do you know the cosine law? What grade level is this ?
February 3, 2015

algebra
I assume you meant: √(6x^3) * √(18x^2) = √(108x^5) = √36*√3*√x^4*√x = 6*√3*x^2*√x = 6√(3x)x^2 = 6x^2√(3x) I don't know how you fudged that answer looking at your second line, which is totally wrong it should...
February 3, 2015

algebra
the way you typed it, it becomes 5/2176782336 * 2/9 I seriously doubt that you intended that. Are you sure you don't have a typo ?
February 3, 2015

algebra
You must know the first few perfect squares, such as 4, 9, 16, 25,... perhaps up to 144 so for √(any number) , attempt to split the number into factors containing one or more of those perfect squares. e.g. √18 = √9 √2 = 3√2 √35 = √5&#...
February 3, 2015

Math (PreCalculus)
write it this way: (sec^2 x - 1)/sinx = tanxsecx In your repertoire of basic trig formulas you should have sec^2 x = tan^2 + 1 LS= (tan^2 x + 1 - 1)/sinx = (sin^2 x/cos^2 x)(1/sinx) = sinx/cos^2 x = (sinx/cosx) (1/cosx) = tanx secx = RS
February 3, 2015

MATH
a = 5 last term = 61 sum(n) = (n/2)(first + last) 957 = (n/2)(5 + 61) 1914 = 66n n =29
February 3, 2015

Math
correct so far You have only found the value of y, you still have to find x sub y = 2 into either of the original equations to find x
February 3, 2015

Math
both sinx and cosx are defined for every value of x the problem occurs with the reciprocal functions such as secx or 1/cosx and cscx also since tanx = sinx/cosx, tanx is undefined if cosx = 0, such as x=90° or π/2 similarly cotx runs into problems when sinx=0 ,such as...
February 3, 2015

Math
you were on the right track. look at these two columns n r , where r is the remainder after dividing by 5 1 3 2 4 3 2 4 1 5 3 6 4 7 2 8 1 9 3 10 4 11 2 12 1 So the remainders cycle as 3 4 2 1, so if n is evenly divisible by 4 , the remainder of 3^n divided by 5 will be 1 if n ...
February 3, 2015

Algebra 2
You have to know how to complete the square. f(x) = -x^2 - 3x = -(x^2 + 3x +9/4 - 9/4) = -( (x + 3/2)^2 - 9/4) = -(x + 3/2)^2 + 9/4 take it from there, all the information is just there in front of you for you 2nd problem, [f o g o h] (-2) means f(g(h(-2))) to me = f(g(-8)) = ...
February 3, 2015

typo - Math
that last line should say y = 3.5
February 3, 2015

Math
let the speed of the boat in still waters be x mph let the speed of the current be y mph So going downstream or with the current the speed is x+y going against the current the speed is x-y so 40/(x+y) = 4 4x + 4y = 40 x + y = 10 , #1 and 40/(x-y) = 5 5x - 5y = 40 x-y = 8 , #2 ...
February 3, 2015

College Algebra
Just realized that I did this same question back in 2007, (and got the same answer) http://www.jiskha.com/display.cgi?id=1195533760
February 3, 2015

College Algebra
time for 1st trip = 200/55 = 40/11 hrs time return trip = 200/40 = 5 hrs avg speed = 400/(5+40/11) = 880/19 mph or appr 46.3 mph
February 3, 2015

Math
so we have this pattern: 1 5 2 11 3 18 4 26 notice that on each consecutive day, the increase is one more than the previous day's increase, suggesting a quadratic expression let number = an^2 + bn + c , were n is the number of days if n = 1: a+b+c = 5 if n = 2: 4a + 2b + c...
February 3, 2015

math
ar = 16 ar^4 = 2 divide the 2nd equation by the first ar^4/ar = 2/16 r^3 = 1/8 r = 1/2 back in first: ar= 16 (1/2)a = 16 a = 32
February 3, 2015

algebra
y^2 - 12y + 31 = 0 clearly , it does not factor, so let's use the formula y = (12 ± √20)/2 = (12 ± 2√5)/2 = 6 ± √5 So what do you think?
February 3, 2015

college algebra
number of rows --- x number of seats per row --- x+8 x(x+8) = 1920 x^2 + 8x - 1920 = 0 (x-40)(x+48)=0 x = 40 or x = -48, which of course makes no sense there are 40 rows, and each row has 48 seats
February 3, 2015

Math Homework
you want to use these identities http://www.mathwords.com/s/sum_to_product_identities.htm especially this one sinx - siny = 2cos( (x+y)/2 )sin(( x-y)/2 ) sin 5π/4 - sin3π/4 = 2cos(π)sin(π/4) = 2(-1)(√2/2) = -√2
February 3, 2015

Math - Answer Check
http://www.jiskha.com/display.cgi?id=1422926711 How can I tell without seeing your calculations ?
February 3, 2015

math
(1/36)^(w+2) = (1/216)^(4w did you realize that 36 = 6^2 and 216= 6^3 (1/6^2)^(w+2) < (1/6^3)^(4w) 6^(-2(w+2)) < 6^(-3(4w)) 6^(-2w-4) < 6^(-12w) then -2w-4 < -12w 10w < 4 w < 4/10 or w < 2/5 or .4
February 3, 2015

Trigonometry
I tried your #1 with x=10° and it did not work so it is not even an identity #2 and #3. you will have to remember that cos 2A = 1 - 2sin^2 A , and sin 2A = 2sinAcosA or cosx = 1 - 2sin^2 (x/2) , and sinx = 2sin(x/2)cos(x/2)
February 3, 2015

correction - Math
I should have read your question a bit more carefully It asked for the equation of the lines perpendicular to the line joining the points Now the question makes even less sense, since we don't know through which point our perpendicular will pass Your answers appear to find...
February 3, 2015

Math
Are those supposed to be your answers ? None make any sense, since it asked for the equation of the line I will do a) 2 points (1,4) and -1,1) slope = (1-4)/(-1-1) = -3/-2 = 3/2 , note that the brackets in the first calculation are essential using the point (1,4) y-4 = (3/2)(x...
February 3, 2015

linear algebra
My explanation of step 4 of my method is not as clear as I intended. The webpage I gave you states it better and shows the pattern Btw, if you had a 4 by 4 you better get several sheets of paper, since you have to bring it from a 4 by 4 to a 3 by 3, that alone would involve 16...
February 3, 2015

linear algebra
There are several ways to find the matrix, here is my method 1. find the determinant of A, I go det(A) = 1 2. flip the matrix along its top-left to bottom-right diagonal to get -5 -3 -9 2 1 3 2 1 4 3. replace each of the terms of this matrix by its cofactors e.g -5 is replaced...
February 3, 2015

Math
recall that cos (2x) = 1 - 2sin^2 x or cos x = 1 - 2sin^2 (x/2) then yours is ... sin (x/2) = 1 - (1 - 2sin^2 (x/2)) sin (x/2) = 2sin^2 (x/2) 2sin^2 (x/2) - sin (x/2) = 0 sin x/2(2sin x/2 - 1) = 0 sin (x/2) = 0 or sin(x/2) = 1/2 case 1: sin (x/2) = 0 x/2 = 0 , π, 2π ...
February 3, 2015

Math Help
Even though you got the correct answer you did not follow the required method. (That's like winning a 100 m backstroke race by using the butterfly stroke , you would be DQ'd) It said to use the Half-Angle formula There are two, sin (2A) = 2sinAcosA and cos(2A) = cos^2 ...
February 3, 2015

maths surds please help and explain
Ok, so you are saying a. 1/√a + 2 = (1/√a)(√a/√a) + 2 = (√a)/a + 2 b. still not clear if you meant √(18/25) or √18 /25 for first interpretation: = 3√2/5 for 2nd interpretation: = 3√2 /25 c). I will take the original as ...
February 3, 2015

maths surds please help and explain
e) is the only one not ambiguous, √5*(√72/√3) = √5*√24 = √120 = 2√30 Also your use of x is not consistent in c) you are using x as a multiplier, in d) you are using x as a variable if you have to show a multiplication signs, either use...
February 3, 2015

maths surds please help and explain
you really have to use brackets to establish the order of operations you want. e.g. in #1, the way you typed it it would be (1/√a) + 2 but I sense you meant 1/(√a + 2) in b) did you mean √(18/25) ? etc
February 3, 2015

algebra
You have 3 terms, two of which contain the common factor (2a-b) Is that -8 at the end supposed to be a multiplier ? The way you typed it, it does not factor.
February 3, 2015

math
speed = distance / time clearly the car went 123 miles in 2 hours so speed = ?????
February 2, 2015

math
width --- x length --- 4x x(4x) = 144 x^2 = 36 x=6 width = 6 ft, length = 24 ft check: area = 6x24 = 144
February 2, 2015

MATH
David Lane's webpage is perfect for this type of question and replaces the charts and tables found in the back of textbooks http://davidmlane.com/hyperstat/z_table.html Just fill in the data for c) remember that 96% would be shorter. You might want to use the second ...
February 2, 2015

Calculus - Differentiation
I would write it as y = 3(1 - 6x^4)^-1 , and use the chain rule dy/dx = -3(1 - 6x^4)^-2 (-24x^3 = 72x^3/(1 - 6x^4)^2
February 2, 2015

Math - Answer Check
translation is correct scale factor of radii is 2 scale factor of area is 4 , you didn't say what scale factor
February 2, 2015

Math - Answer Check
Your question makes no sense to me. All circles are "similar" to each other.
February 2, 2015

calculus
f(x) = 2x + sin(2x) f ' (x) = 2 + 2cos(2x) = 0 2cos(2x) = -2 cos 2x = -1 I know cos π = -1 so 2x = π x = π/2
February 2, 2015

calculus
after 1 sec, d = 6(1) + 2 = 8 after 4 sec, d = 6(16) + 2(4) = 104 avg velocity = total distance/total time = (104-8)(4-1) = 32 miles/hr
February 2, 2015

geometry
done, check back to your previous post of this. Btw, have some patience. You only gave the other one about 10 minutes for a response.
February 2, 2015

Geometry
Let's assume that they are in the same line of sight, that is, the two ships and the lighthouse are in the same plane. Label the farther ship A and the nearer ship B Label the top of the lighthouse L and its bottom M I see the following angles, angle A = 20° angle LBM...
February 2, 2015

math
I assume that some of the numbers can be the same, otherwise the least possible multiplication would be 1x2x3x4x5x6 = 720 so to get 36 using the smallest possible numbers would be 1x1x2x2x3x3 and the least possible sum = 15
February 2, 2015

Vectors
you made an error in the initial addition. 2a = 6x + 4y b = 5x - 4y add them: 2a + b = 11x x = (2a+b)/11 or 2a/11 + b/11 , which is the given answer now plug the x back into the first equation: 5x - 4y = b 5(2a+b)/11 - 4y = b times 11 5(2a + b) - 44y = 11b 10a + 5b - 44y = 11b...
February 2, 2015

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