Tuesday
February 9, 2016

Posts by Reiny

Total # Posts: 32,875

Calculus help
Following bob's own suggestion, it should have been: y = √ ( (x^2 + 3x + 4)^2) = [( (x^2 + 3x + 4)^2)]^(1/2) dy/dx = (1/2) ( (x^2 + 3x + 4)^2)^(-1/2) (2)(x^2 + 3x + 4) (2x+3) = (2x+3)√(x^2 + 3x + 4) or we could do it piece-meal y=|x^2+3x-4| --> y = x^2 + 3x...
January 15, 2016

math
There are three sides, and they are all equal, so .....
January 15, 2016

Math
Were you just guessing ? Had you checked you would have been able to answer the question. How did you decide it was c ?
January 15, 2016

Geometry
correct
January 15, 2016

math
hint: the LCD is 24
January 15, 2016

geometry
length --- x width ---- y height ---- 6 volume = 6xy The most common definition of lateral surface is the sum of all the surfaces of the object except the base. So the sum of all six sides of our box is 198 the sum of the 5 sides , that is, excluding the base , is 144 so the ...
January 15, 2016

let's try again
or: 321base 4 = 3(4^2) + 2(4) + 1 = 48 + 8 + 1 = 57 in base 10 23base 4 = 2(4) + 3 = 11 in base 10 57/11 = 5 2/11 so the remainder in base 10 is 2 and since 2base 4 = 2base 4 R = 2 Steve's method is more direct, however you have to know how to do arithmetic in base 4.
January 15, 2016

Help!!! Maths number base
or: 321base 4 = 3(4^2) + 2(4) + 1 = 48 + 8 + 1 = 57 in base 10 23base 4 = 2(4) + 3 = 11 in base 10 57/11 = 5 2/11 so the remainder in base 10 is 2 and since 2base 4 = 2base 10 R = 2 Steve's method is more direct, however you have to know how to do arithmetic in base 4.
January 15, 2016

Math
money spent in first store = (1/2)x + 14 money spent in 2nd store = (1/3)x + 14 so (1/2)x + 14 + (1/3)x + 14 =x times 6 , the LCD, to clear fractions 3x + 84 + 2x + 84 = 6x x = 168 check: amount spent in store 1 = 84 + 14 = 98 money spent in store 2 = 56+14 =70 he spent 98+70...
January 14, 2016

math
follow the order of operation, which you should memorize (BEDMAS) 6³ + 6 ÷ 2¹ - 4² = 216 + (6 ÷ 2) - 16 = 216 + 3 - 16 = 203
January 14, 2016

damon i need your help again
Looks like Damon is not online right now I = PRT (300)(.0134)T = 300 .0134T = 1 T = appr 75
January 14, 2016

Math
1st --- x 2nd --- x+8 3rd ----2(x+8) solve for x x + x+8 + 2(x+8) = 92
January 14, 2016

math
case 1: 3.2% for 5 years, then 4% for 8 years P(1.008)^20 (1.01)^80 = 25000 P = 9616.55 case 2: P(1.008)^32 (1.0125)^68 = 25000 P = 8324.16 clearly since he needs less money to invest using the second option to obtain the same goal, he should clearly take the second option.
January 14, 2016

Math
yup
January 14, 2016

Math
all are good, except the last one 11% of 400 = .11(400) = 44 not any of the choices. Typo ?
January 14, 2016

Math
just use rounding e.g. √56 = 7.48... so to the nearest integer √56 = 7 √78 = 8.83... so to the nearest integer √78 = 9
January 14, 2016

Geometry H
Make an effort to memorize the distance between two points formula D = √( (change in x's)^2 + (change in y's)^2 ) = √( (5+3)^2 + (-6-2)^2) = ...
January 14, 2016

Math
#1 -2(6x-4)= -12x -12x + 8 = -12x 8 = 0 which is false, thus NO solution If you lose your variable and you end up with a FALSE statement, like above, there is no solution If you lose your variable and you end up with a TRUE statement, there is an infinite number of solutions. ...
January 14, 2016

Math
#3 SA = 4πr^2 = 4π(16) = 64π = appr 201 the rest look good
January 14, 2016

math [last]
close ... y = 1/2x + 7
January 14, 2016

math [last]
oh my y = mx + b , where m is the slope and b is the y-intercept.
January 14, 2016

Geometry
slope = change in y / change in x = (-5 + 1)/(2+1) = -4/3 can you see your error ?
January 14, 2016

math
total distance ---- x m (1/4)x + (3/5)(3/4)x + 3600 = x multiply each term by 20 , the LCD 5x + 9x + 72000 = 20x 6x = 72000 x = 12000 m looks like she did a 12 K triathlon
January 14, 2016

math
speed of express ---- x km/h speed of slow train -- x - 12 km/h solve for x 240/(x-12) - 240/x = 1 (saying: the difference in their times = 1 hr and time = distance/rate )
January 14, 2016

Geometry
slope = rise/run the tanØ = slope take it from there.
January 14, 2016

math
You are just guessing at 8 because it is one of the choices, and you are hoping that somebody will just give you the answer. Did you make a sketch? Did you notice that the height is 9 cm, which means that a length of 8 wouldn't even reach the top straight up. How do you ...
January 14, 2016

Math
Haven't done this kind of question in over 50 years. Euler's Formula .... http://www.abecedarical.com/zenosamples/zs_complexnumbers.html
January 14, 2016

Math
the two functions intersect at x = ± .824132 I have no idea what R is supposed to be
January 13, 2016

Math
weight of full basket --- x (2/3)x = 3/4 solve for x
January 13, 2016

Math
let the number of CD's be c solve for c 15.95c = 13.95c + 8
January 13, 2016

Geometry
make your sketch angle at water --- Ø tanØ = 50/750 = 1/15 Ø = appr 3.81° which is also the angle of depression
January 13, 2016

math
1650(1+i)^3 = 2262.7 divide both sides by 1650, take the cube root, then subtract 1 to get i, the annual rate expressed as a decimal. let me know what you got.
January 13, 2016

One Last Help
2. 4 1/4 = 17/4 = 17/4 * 100% = 17(25)% = 425% or 4 = 400% 1/4 = 25% so 4 1/4 = 425% 5. .4% = .4/100 = 4/1000 = 1 250 the rest are correct
January 13, 2016

Math
let z = 2 + 3i for the angle, tanØ = 3/2 Ø = .98279 radians so z = √13(cos .98279 + isin .98279) then z^6 = √3^6(cos 6(.98279) + isin 6(.98279) ) = 27(cos 5.89676 + i sin 5.89676) = appr 25 - 10.18 i or in short form: 27 cis 5.89676 If you need the ...
January 13, 2016

math
I found 3 of them: 798 , 1726, and 2654 How? Using a silly very old computer language program from the 80's called BASIC 1 dim x(100),y(100) 10 for n = 1 to 100 20 x(n) = 32*n+30 30 y(n) = 58*n+44 50 next n 60 for k = 1 to 100 70 for l = 1 to 100 80 if x(k) = y(l) then ...
January 13, 2016

Math
your choice is totally illogical. How can their combined weight be less than each of the parts ?? Are you just guessing, hoping for somebody to just tell you the answer?
January 13, 2016

MATHEMATICS
you listed 3 events, so prob = 3/6 = 1/2
January 13, 2016

mathematics number systems
1.244444... = 1 + .24444.... = 1 + (24-2)/90 = 1 + 22/90 = 1 + 11/45 = 56/45 check with a calculator, it is correct or let x = 1.244444 time 10 10x = 12.4444... x = 1.244444. -------------- subtract: 9x = 11.2 x = 11.2/9 = 112/90 = 56/45
January 13, 2016

math
There is really no problem with your solution, other than the fact it seems too complicated. e.g. in the slope, compare your steps with mine instead of saying: (1,20) = x , say ... for the given point (1,20), x = 1 and y = 20 notice you have the same equation as I have.
January 13, 2016

math
wow. slope = (4.5-20)/(8-1) = -15.5/7 ----> top and bottom times 10 = -155/70 = -31/14 so y = (-31/14)x + b sub in the point (1,20) 20 = -31/14 + b b = 20 + 31/14 = 311/14 y = (31/14)x + 311/14 you are correct, I object to the statement: (1,20) = x, it is meaningless
January 13, 2016

Math (and note to DAMON)
you got it
January 13, 2016

Math (and note to DAMON)
#3 1/5 = .2 so 1/5 % = .2 % = .002 #4 .75 % = .75/100 = 75/10000 = 3/400 , -------- your 3/4 would be 75% 9. since 1 ---> 100% 3 ----> 300% the rest are correct
January 13, 2016

Math
#9 p/8 ≥ -5 multiply both sides by +8, thus no reversal of inequality sign p ≥ -40 the rest are correct
January 13, 2016

math
new dimensions: .7(15) and .7(12) new area = 10.5(8.4) = 88.2 yards^2 path = 15(12) - 88.2 =appr ......
January 13, 2016

finance
amount to mortgaged = .9(120000) = 108000 i = .062/12 = .0051666... n = 30(12) = 360 P( 1 - 1.00516666..)^-360)/.0051666.. ) = 108000 you do the button-pushing ( hope you get 661.47 )
January 13, 2016

MATH
Prob(all wrong) = (4/5)(1/3)(3/5) = 12/75 = 4/25 prob(at least one) = 1 - 4/25 = 21/25 prob(only one correct) ---> RWW, WRW, WWR = (1/5)((1/3)(3/5) + (4/5)(2/3)(3/5) + (4/5)(1/3(2/5) = 3/75 + 24/75 + 8/75 = 35/75 = 7/15 check my arithmetic
January 13, 2016

mathematics
boys wearing glasses = 24 boys not wearing glasses = 36 girls wearing glasses = 21 girls not wearing glasses = 19 1) prob(a student wears glasses) = 45/100= 9/20 2) 19/40 3) ... can you see what I am doing? take over
January 13, 2016

maths
term(8) = a + 7d but a = 3 so 3 + 7d = 31 take over
January 13, 2016

math
The "pattern" is that for each increase of 5 in the input, the output increases by 1 now can you write that as a relation between x and y ?
January 13, 2016

Algebra
Several ways: 1. Heron's Formula, google it and apply 2. - find the equation of one of the sides and write it in the form Ax + By + C = 0. - find the length of the line used to find the equation. - Use the method of finding the distance from a point to a line. - You now ...
January 13, 2016

Algebra
I assume you know how to find the distance between two points. I will do the first length, you do the rest. from (-2,-7) to (1,-6) distance = √( (-2-1)^2 + (-7+6)^2 ) = √( 9 + 1) = √10 after finding the other two, add them up
January 13, 2016

Math
The question is poorly worded. "Which would be the best design for an ice cube?" based on what? Given some fixed surface area ? - which is rather meaningless for an ice "cube" Stability of storing? - trays to freeze spherical ice "cubes" don't...
January 13, 2016

Math
Still not totally clear what you mean, is it f(g(x)) or g(f(x)) ------ not the same! I will assume f(g(x)) = f(3-x) = 2^(3-x) I have no idea how you got 3x^2 + 12 same with B if f(x) = sinx and g(x) = x then f(g(x)) = f(x) = sinx
January 13, 2016

Math
You got 3x^2 + 12 , but what was the question ??? Are you supposed to find something like f(g(x)) ? Are you solving ?
January 13, 2016

maths
number of selections with no restrictions = C(11,6) = 462 We can't have: zero red, 1 red, zero black, 1 black which would be C(5,0)xC(6,6) + C(5,1)xC(6,5) + C(6,0)xC(5,5) + C(6,1)xC(5,4) = 1x1 + 5x6 + 1x1 + 6x5 = 62 prob(your event) = (462 - 62)62/462 = 200/231
January 13, 2016

MATH
a) this is simply a straight line with y-intercept of 2000 and a slope of 6000 I would scale my graph so each vertical unit (the y) represents 1000 dollars, and each horizontal unit , the x's, represents the number of miles. b) think in thousands only. Can you mentally ...
January 13, 2016

math
money at beginning --- x money spent in store A = x/2 + 50 amount left after shopping in A = x - x/2 - 50 = x/2 - 50 money spent in store B = (1/2)(x/2 - 50)+100 = x/4 - 25 + 100 = x/4 + 75 amount left = x/2 - 50 - (x/4 + 75) = x/4 - 125 but that is 250 x/4 - 125 = 250 x/4 = ...
January 13, 2016

math
area of pond = π(13)^2 = 169π area of the whole thing = π(15)^2 = 225π area of "ring" = 225π - 169π = ... square yards and each square yard costs $50, so .... take over
January 12, 2016

Algebra II
625^3/4 = (√ (√625) )^3 = (√25)^3 = 5^3 = 125 by definition of the square root operation: return the positive square root of the number e.g. √4 = 2 , even your calculator is programmed that way as opposed to x^ = 4 We usually write as our next step x...
January 12, 2016

Math
All are good except #7 g/-5 < -18 to "clear" the -5, we multiply both sides by -5, thus reversing the inequality sign g > +90 , which is C (looks like you added the -5)
January 12, 2016

Math
white marbles --- 2x blue marbles ---- 3x 5x > 20 x > 4 so pick any value of x > 4, say x = 8 then whites = 16 blues = 24 notice 16:24 = 2 : 3 and 16+24 > 20 you could pick as many combinations as you want.
January 12, 2016

Calculus AB
looks like the Mean Value Theorem Here is a good video by Khan, where he explains your problem is very simple terms https://www.khanacademy.org/math/differential-calculus/derivative-applications/mean_value_theorem/v/mean-value-theorem
January 12, 2016

math help
I am interpreting " an increase of -6 per hour" to mean a decrease of 6° per hour. "Which of the following ..." has no following. I would expect to see something like temperature = -6t - 13, where t is the number of hours past 1:00 pm on Tuesday.
January 12, 2016

Math
since (21)(y) is the same as 18(y+7) , let's say so: 21y = 18(y+7) 21y = 18y + 126 3y = 126 y = 42 so ......
January 12, 2016

Math
since you have 3 unknowns you will need 3 distinct equations. I see only two. so all you can do is say: 2a + c = 25
January 12, 2016

Math
time until they pass in the sky --- x hours so 200x + 300x = 780 take over
January 12, 2016

Math(Algebra)
price of senior ticket --- x price of student tickets -- y day 1: 8x + 12y = 160 day 2: 11x + 6y = 115 day 1 equation ÷ 2 4x + 6y = 80 subtract from day 2 equation: 11x + 6y = 115 4x + 6y = 80 -------------- 7x = 35 x = 5 back in 4x+6y = 80 20 + 6y = 80 6y = 60 y =10 ...
January 12, 2016

Math
#3 is wrong if 1 yd = 3 ft then 100 yd = 300 ft
January 12, 2016

trigo
Did you make a sketch? I labeled the tower as PQ, with Q and the extended line of AB In triangle PAB angle A = 42°, angle ABP = 130° then angle APB = 8° by sine law: BP/sin42 = 30/sin8 BP = 30sin42/sin8 In the right-angled triangle BPQ sin50 = PQ/BP PQ = BPsin50...
January 12, 2016

Math6/7
yes
January 12, 2016

Calculus
let the number of 100 decreases be n number sold = 5000 + 1500n selling price per item = 900 - 100n return = (5000+1500n)(900-100n) = 500(10 + 3n)(100)(9 - n) = 50000(90 + 17n - 3n^2) d(return)/dn = 50000(17 - 6n) = 0 for a max 6n = 17 n = 17/6 = appr 2.8 assuming we can only ...
January 12, 2016

math
First see my correction to your previous question of this type http://www.jiskha.com/display.cgi?id=1452575743 if the ratios of the radii is in the ratio of 1 : n then the ratio of their areas is 1 : n^2 that is, if the radius is multiplied by a factor of n, where n is a whole...
January 12, 2016

math
original workforce --- x .125x= 4000 x = 32000 workforce after layoffs = 32000-4000 = 28000
January 12, 2016

Calculus
f(x) has an absolute minimum of 0 because of the definition of the square root. Since we cannot take the square root of a negative number, x-3 ≥ 0 x ≥ 3 and f(3) = 0 and f(x) only starts at x = 3 If you sketch y = √(x-3) , there are no points below the x-axis...
January 12, 2016

correction - math
area of bulls-eye = π(1.5)^2 = 2.25π area of whole target = π(7.5)^2 = 56.25π so the bull's-eye is 2.25π/56.25π = 1/25 which reflects the property that the areas of different circles are proportional to the square of their corresponding ...
January 12, 2016

math
8 letters with 2 E's, 2 D's number of permutations = 8!/(2!2!) = 10080
January 12, 2016

math
As Damon said, complex roots come in conjugate pairs. Using properties of roots: sum of our roots = 3+4i + 3-4i = 6 product of roots = (3+4i)(3-4i) = 9 - 16i^2 = 25 p(x) = x^2 - 6x + 25
January 11, 2016

Math
#1. two distinct parallel lines, so no solution #2, correct #3. If you multiply the first by 3, you get the 2nd. So the two equations are really one and the same, thus : infinite number of solutions.
January 11, 2016

Math
All are correct, good job
January 11, 2016

Algebra
Since both equations contain 65y, subtractions would make the y's go away subtract the first equation from the 2nd to get 991x = 208 x = 208/991 sub back into the first: 234(208/991) + 65y = 219 65y = 219 - 48672/991 = 168357/991 y = 168357/64415
January 11, 2016

Math
solve for x, where x is the amount of 12% acid .12x +0(3) = .07(x+3)
January 11, 2016

alligation and mixture
let the amount of water to be added be x L looking at the amount of acid we have: .20(25) + 0(x) = .10(25 + x) solve for x
January 11, 2016

Math PLEASE HELP!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Sorry my musical friend, there are no diagrams visible in this format
January 11, 2016

Calculus AB
I will assume those were exponents and you want: f(x) = 3x^(1/3) + 6x^(4/3) f ' (x) = x^(-2/3) + 8x^(1/3) f '' (x) = (-2/3)x^(-5/3) + (8/3)x^(-2/3) checking your work: x^(-2/3) (1 + 8x) = 0 x = -1/8 , you had that! but that is only the x of the extrema point so f(-...
January 11, 2016

Calculus AB
all looks good Also the reason we reject x = 12 ... one of the sides would be (16-24) which is negative.
January 11, 2016

Quadratic Equations
Your quadratic must have been D = -5t^2 + 324 If we just care about the distance covered d = 5t^2 so when t = 1, d = 5 when t = 2 , d = 20 when t = 3 , d = 45 You had those correct. distance covered in the last second: Since your last second is the third second take the ...
January 11, 2016

Math,algebra,age question
Son's present age --- x Man's present age --- 4x 16 years from now: son --> x+16 man --> 4x+16 solve .... 4x+16 = 2(x+16)
January 11, 2016

math
Factor the LS as a difference of cubes LS = (cos^2 A - sin^2 A)(cos^4 A + (sin^2 A)(cos^2 A) + sin^4 A) = cos (2A) (cos^4 A + sin^4 A + 2(sin^2 A)(cos^2 A) - (sin^2 A)(cos^2 A) ) = cos (2A) ( (cos^2 A + sin^2 A)^2 - sin^2 A cos^2 A ) = cos(2A) ( 1 - sin^2 A cos^2 A ) getting ...
January 11, 2016

Math
7x - 14y = -8 has a slope of 1/2 so the perpendicular must have a slope of -2 none of your choices have a slope of -2 I suspect a typo in your answer choices.
January 10, 2016

Math
The equation you need takes the form y = mx + b, where m is the slope. So let's find the slope first ... slope = (2-1)/-3-(-6)) = 1/3 so we have y = (1/3)x + b but (-6,1) lies on it, 1 = (1/3)(-6) + b 1 = -2 + b b = 3 equation: y = (1/3)x + 3 I usually check by subbin in ...
January 10, 2016

math
"..... and intercepts y-axis with 8 units." this makes no sense to me Do you mean it touches at (0,8) ?
January 10, 2016

Math
S = 2d + 13 , where S is the number of situps, d is the number of days, d≥1 , d is an integer. check: if d = 1, (first day) , S = 15 if d = 2 (2nd day) , S = 17 yup that works so if S = 33 33 = 2d + 13 2d = 20 d = 10 We could arrange the equation: 2d + 13 = S 2d = S - 13...
January 10, 2016

Trig - 9th grade
I had actually followed the same method Steve suggested. My first 4 lines were an alternate attempt, which does not fit in with the rest of the solution. I should have deleted those 4 lines. As Steve pointed out it was a mess, and I had to use Wolfram http://www.jiskha.com/...
January 10, 2016

Pre-calc
5(2sinxcosx) + 3sinx - 1 = 0 sinx(10cosx + 3) = 1 we know sinx = cos(90°-x) , so cos(90-x)(10cosx + 3) = 1 10sinxcosx = 1 - 3sinx 100sin^2 x cos^2 x = 1 - 6sinx + 9sin^2 x 100sin^2 x (1 - sin^2 x) = 1 - 6sinx + 9sin^2 x 100sin^2 x - 100sin^4 x + 6sinx - 9sin^2x - 1 = 0 let...
January 10, 2016

MATH Precalculus
let amount = c e^(kt), where c is the starting amount, and t is in hours, and k is a constant. In our case c = 150 given: when t = 26, amount = 75 75 = 150 e^(26k) .5 = e^(26k) 26k lne = ln .5 26k (1) = ln .5 k = ln .5/26 = appr -.0266595 then: amount = 150 e^(-.266595t) so ...
January 9, 2016

Geometry
under reflection in y = -x (-3,7) ----> (-7,3) with a dilation of 3 at the origin (x,y) --->(3x,3y) (-7,3) ----> (-21,9)
January 9, 2016

math
solve for x: .1(2x) + .07x = 94.50
January 9, 2016

Geometry
8 x 1 = ... 8 x 1.25 = ....
January 9, 2016

Maths
the diagonals of a rhombus right-bisect each other, so make a sketch and look at the right-angled triangle with angle 38° (half the 76) and leg of 4 cm The hypotenuse is the side of the rhombus, call it x sin 38° = 4/x x = 4/sin38 = appr. 6.487 cm = appr 65 mm
January 9, 2016

Math
Maybe setting up a ratio makes sense to you ... x/15 = 77.28/4 x = 15(77.28/4) which is Damon's calculation.
January 9, 2016

  1. Pages:
  2. <<Prev
  3. 1
  4. 2
  5. 3
  6. 4
  7. 5
  8. 6
  9. 7
  10. 8
  11. 9
  12. 10
  13. 11
  14. 12
  15. 13
  16. 14
  17. 15
  18. Next>>