Saturday
December 20, 2014

Posts by Reiny


Total # Posts: 28,261

algebra
Really ???? 10-4x = 0 -4x = -10 x = -10/-4 = 2.5
October 19, 2014

tech math
let the diameter of the small pulley be d let the diameter of the larger pulley be d+7 belt distance covered by smaller pulley in one minute = 136(πd) = 136πd by the larger pulley = 80(π)(d+7) so 136πd = 80π(d+7) divide out the π 136d = 80d + 560 ...
October 19, 2014

Business Math
work on the loan option: balance owing = 7200-720 = 6480 let the monthly rate be x then 205( 1 - (1+x)^-36)/x = 6480 205(1 - (1+x)^-36) = 6480x Equations of this type are very difficult to solve, since there is no "formula" to handle it. In the "olden" days...
October 19, 2014

Calculus
I would have taken the first derivative of -1/(1-x) and simplified it to 1/(x-1) or (x-1)^-1 (If my numerator or my denominator is a constant, I seldom use the quotient rule, since one part drops out anyway) y' = (x-1)^-1 y'' = -1(x-1)^-2 = -1(x-1)^2 f '' (...
October 19, 2014

Maths
recall two properties 1. for y = abc y' = abc' + acb' + bca' etc for multiple factors **** However, if any of the a, b, or c are powers such as (c-4)^4 , then that base of x-4 will appear in each of the terms of y'' ***** very important ! 2. if y'&#...
October 19, 2014

Steve or Damon or bobpursly or ... - Calculus
not quite, your brackets are very important what you have worked out is ... ln (x^x) which is x lnx etc, and your answer would be correct for that but you typed (lnx)^x which would be (lnx)(lnx)(lnx) ... (lnx) , x times we might apply the rule: extension of the product rule if...
October 19, 2014

AP Calc. AB
1. take the derivative of each, not that bad If you have a calculator, just plug in each given value and see what happens or make a sketch of y = sin^2 (x) and y = (1/2)x^2 from appr -1.6 to +1.6 take a few points using your calculator . 2. Did you get the actual derivative? I...
October 19, 2014

Maths
let's use an intuitive approach You might recall that lim (1 + 1/n)^n = e as n ---> ∞ or lim (1 + n)^(1/n) = e , as n ---> 0 now we have (1+sinx)^(1/tanx) now as x ---> 0 , sinx --->0 and 1/tanx ----> ∞ so we have (1 + really small)^really large ...
October 19, 2014

College Algebra (Word Problem)
What's an eld ? let the side parallel to the rive by y ft let the other sides be x ft each so xy = 1200 y = 1200/x cost of fence = 16y + 8(2x) = 16(1200/x) + 16x = 19200/x + 16x d(cos)/dx = -19200/x^2 + 16 = 0 for a min cost. 16x^2 = 19200 Can you finish it?
October 19, 2014

Math
What is 5x5x4
October 18, 2014

math
Use the distance between 2 points formula ... d = √( (4 - (-2))^2 + (-6-2)^2 ) = √(36+64) = √100 = 10
October 18, 2014

algebra
I will assume you want A(w) = √(w^2+13) then A(0) = √(0+13) = √13
October 18, 2014

algebra
wherever you see an x, plug in x+5 f(x+5) = 6(c+5)^2 + 7 = 6c^2 + 60c + 157
October 18, 2014

Math
amount of 36% solution -- x cc amount of 14% solution -- (25-x) cc .36x +.14(25-x) = .25(25) times 100 , (don't like decimals like to avoid them) 36x + 14(25-x) = 25(25) 36x - 14x = 625 - 350 22x = 275 x = 12.5 cc so it looks like 12.5 cc of each
October 18, 2014

math
let the number have the form abc "the first and second digits are multiple of 3 the first digit is greater than the second digit." ---> has to be 63c or 963, would also consider 30c "the sum of the first two digits is 7 more that the third digit " -->...
October 18, 2014

Algebra
difference of squares ... ( (y+2) + 9)( (y+2) - 9) = (y+11)(y-7)
October 18, 2014

Algebra
without "calculating", I can tell that the question is bogus, since only one point is given. Can't find slope if given only one point.
October 18, 2014

Intermediate Algebra
If they have to do their OWN homework, then the question really makes no sense. If it is an assignment type homework were both can work on the project, then beth's rate = 1/6 nina's rate = 1/9 combined rate = 1/6 + 1/9 = 5/18 time at combined rate = 1/(5/18) = 18/5 or ...
October 18, 2014

Algebra
2x^2-5x^3-20x^2+115x-52=0 -5x^3 - 18x^2 + 115x - 52 = 0 5x^3 + 18x^2 - 115x + 52 = 0 no obvious NICE factors the graph suggests 3 real roots, thus no complex zeros http://www.wolframalpha.com/input/?i=5x%5E3+%2B+18x%5E2+-+115x+%2B+52+%3D+0 I suspect a typo
October 18, 2014

Algebra Help
interpretation: 4 roots: 2+2i 2-2i -5 -5 the -5 root twice yields (x+5)^2 for the two complex roots: sum of those two = 4 product of those two = (2+2i)(2-2i) = 8 which gives us the trinomial x^2 -4x + 8 so f(x) = a(x^2 - 4x + 8)(x+5)^2 , where a is any non-zero constant
October 18, 2014

Scientific notation
correct, use 10^4 to show 10 raised to the fourth
October 17, 2014

Scientific notation
the format is to always have a single non-zero digit, followed by a decimal place time a power of 10 69,000,000,000 = 6.9 x 10^10 , exponent is 10 since we moved our decimal 10 places
October 17, 2014

finance
let the quarterly rate be i then 1(1+i)^12 = 3 (1+i) = 3^(3/12) = 3^(1/4) = 1.316 i = .316 or appr 31.6 % per quarter, or appr 126.4% per annum quickly, tell me who is giving us that, I have a few dollars to invest.
October 17, 2014

diff calculus
let the length of the rectangle parallel to the 160 ft side be x let its height be y I see 3 similar triangles, the original and the 2 smaller triangles by ratios: y/(160-x) = 120/160 = 3/4 4y = 480 - 3x y = 120 - 3x/4 area of rectangle = A = xy = x(120 - 3x/4) = 120x - 3x^2/4...
October 17, 2014

algebra 1
no first of all your answer, if that number is supposed to be the answer, is incorrect secondly, I do not like the way you present your answer proper way: 4 = 18 - 3w 3w = 18-4 3w = 14 w = 14/3 or 4 2/3
October 17, 2014

math
did you make a sketch? Isn't it just 5 km due west of where it started from without doing any calculations?
October 17, 2014

Algebra2
the given line has slope -2/3 so your perpendicular line has slope 3/2 new line must be y = (3/2)x + b passing through (-4,3) 3 = (3/2)(-4) + b b = 3 + 12/2 = 9 new line: y = (3/2)x + 9
October 16, 2014

Math
You want the sum of "all " the terms an infinite GS you have a GS, where a = 4/3, r = 1/2 sum(of all the terms) = a/(1-r) = (4/3)/(1-1/2) = (4/3)/(1/2) = 8/3 or 2 2/3
October 16, 2014

calculus
I will ignore the hint and use a very straight-forward method the shortest distance will of course be the normal to the plane going through (1,0,0) plane: 6x + 9y - z + 1 = 0 a normal to the plane is (6,9,-1) and passing through (1,0,0) would be the line x = 6t + 1 y = 9t z...
October 16, 2014

Math
That will depend on what type of sequence we are looking at Is it AS ? Is it GS ? or is it ...?
October 16, 2014

calculus
forget the very last line, I had made corrections, but forgot to delete that line
October 16, 2014

calculus
Last time I did this type of question was 55 years ago, so I hope I can remember. I think we first have to find the area intercepts between y = 25x^2 and y = 4 25x^2 = 4 x = ± 2/5 by symmetry we can go from 0 to 2/5 and double area = 2(integral) (4 - 25x^2) dx from 0 to...
October 16, 2014

Algebra2
were did you get 2^7i from ??? I thought we did 2 i^7 and I thought I did that for you. i^100 = (i^4)^25 = (+1)^25 = 1 I strongly suggest your write down the first 4 or 5 terms of the pattern I gave you and I strongly suggest you read my explanation of that pattern.
October 16, 2014

Algebra2
I assume you want to simplify each one the imaginary number i has very unusual properties watch this cyclic pattern: i i^2 = -1 i^3 = i(i^2) = -i i^4 = i^2 i^2 = (-1)(-1) = +1 i^5 = i i^4 = i(1) = i , and here we go round again notice every even power of i is either +1 or -1 ...
October 16, 2014

Algebra
actually the 2nd is a strange one, as it has an infinite number of solutions 3/x = 3x/x^2 the right side simplifies to 3/x so you have 3/x = 3/x, which of course is true for all values of x except x = 0 (remember, we can't divide by zero)
October 16, 2014

Math
correct
October 16, 2014

math
There were 23 marbles, of which 5 were blue 3 were removed, one of them blue so now there are 20 marbles, of which 4 are blue prob(blue) = 4/20 = 1/5 which is C
October 16, 2014

algebra
width --- x length -- 3x+5 area = x(3x+5) or 3x^2 + 5x
October 16, 2014

Math
yes
October 16, 2014

Math algebra Help please
original: base --- b, height --- h area = (1/2)bh = 24 bh = 48 new triangle: base ---6b, height ----6h new area = (1/2)(6b)(6h) = 18 bh = 864
October 16, 2014

Algebra
Let the time for the first train be t hrs 50t + 70(t-1) = 350 120t = 420 t = 420/120 = 7/2 or 3.5 hrs
October 16, 2014

Math
break down of A = [ w | w < 1} A = ------ A is equal to | w ----- the set of all w such that w < 1 ----- w is less than 1 Now "translate" the second one for me
October 16, 2014

Math
check if (2x+2)/(x+1) = (5x+1)/(2x+2) for ALL values of x that is, the equation should reduce to 0 = 0 to be a GS (I know it works for x = 3)
October 16, 2014

Calc
sorry, I forgot the +2xy on the left side should have been dy/dx = (y^3 - 2xy - 12x^2)/(x^2 - 3xy^2) I am disappointed that you could not find that simple error.
October 16, 2014

Calc
4x^3+x^2y-xy^3 = -4 we want derivatives with respect to x, so whenever we get a dx/dx, we get 1 So I will not write the dx/dx 's 12x^2 + (x^2)dy/dx + y(2x) - x(3y^2)dy/dx - y^3 = 0 dy/dx(x^2 - 3xy^2) = y^3 - 12x^2 dy/dx = (y^3 - 12x^2)/(x^2 - 3xy^2) check my work, I tend ...
October 16, 2014

math
correct
October 16, 2014

math
difference = 1/2 - 13/32 = 16/32 - 13/32 = 3/32
October 16, 2014

Calculus
or #1, use r^2 = x^2 + y^2 x^2 + y^2 = 169 2x dx/dt + 2y dy/dt = 0 , I differentiated with respect to t (time) or dy/dt = (-x/y)dx/dt when x = 12, dx/dt = 5 ft/s find dy/dt at that moment 12^2 + y^2 = 169 y = 5 dy/dt = (-12/5)(5) ft/s = -12 ft/sec the negative shows it is ...
October 16, 2014

Maths
y1/y2 = √x1/√x2 1/4 = √x1/√x2 √x2 = 4√x1 square both sides x2 = 16x1 x2/x1 = 16/1 or 1600 % e.g. suppose x = 36 then y = 6 now we want y to be quadrupled, so y = 24 and x would be such that √x = 24 , so x = 576 percentage increase in x...
October 16, 2014

Maths
6 men --- 4 hrs --- 6m deep 1 man ---24 hrs --- 6m deep 10 men 24/10 hrs -- 6 m deep 10 men 2.4 hrs --- 6 m deep 10 men 2.4/6 hrs --1 m deep 10 men .4 hrs ===1 m deep 10 men .4(5) hrs --- 5 m deep 10 men 2 hrs ---- 5 m deep OR it takes 24 manhrs to dig a 6 m deep hole it takes...
October 16, 2014

Math
1. looks like a GS, were a = 2/3, and r = 3 sum(5) = a(r^5 - 1)/(r-1) = (2/3)(3^5 -1)/2 = ..... 2. nope, (4x-2)/(2x) ≠ (6x-4)/(4x-2) for all values of x it would be true or only x = 1 3. 0.7575757575... = .75 + .0075 + .000075 + ... a GS where a = .75, r = .01 sum(...
October 16, 2014

maths
Suppose we had 25600 kg of food or 25600/80 kg per student for 80 days, or 1 kg per student for 1 day so in 20 days, 320(20) kg or 6400 kgwere used so 19200 kg are left for 300 students time for this to last = 19200/300 = 64 days or do the same with a variable let the amount ...
October 16, 2014

Map Rectangle
area on map = 12 cm^2 actual size of rectangle = 4000 cm by 3000 cm or 40 m by 30 m real area = 1200 m^2
October 16, 2014

math
-2/5x - 9 < 9/10 times 10 -4x - 90 < 9 -4x < 99 x > -99/4
October 16, 2014

Math
4cos^2 A - 3cosA = 0 cosA(4cosA - 3) = 0 cosA=0 or cosA = 3/4 but your domain is quadrant II, where the cosine is negative except cos90° = 0 so x = 90° do the 2nd the same way by factoring out tanA
October 15, 2014

Math
first of all, notice that each equation is divisible by 4 new equations: 8x + 9y = -4 9x + 8y = -4 multiply 1st by 8 ---> 64x + 72y = -32 multiply 2nd by 9 --> 81x + 72y = -36 subtract them 17x= -4 x = -4/17 into the 1st:8(-17/4) + 9y = -4 times 4 -136 + 36y = -16 36y = ...
October 15, 2014

St Grainne,s
let the tend digit be 2x then the unit digit and the hundreds digit are each x x+2x+x = 16 4x=16 x = 4 you are 484
October 15, 2014

maths
I will assume you meant to say that the area of the ink blot is growing at the rate of 2 cm^2 /s A = πr^2 dA/dt = 2πr dr/dt 2 = 2π (28/11) dr/dt dr/dt = 11/(28π) cm/sec = appr .125 cm/s
October 15, 2014

math
dozen of pencils --- x dozen of pens ----- y dozen of erasers --- z 4x + 3y + 2z = 16 2x + 4y + 6z = 90 6x + 2y + 3z = 70 Since you want it done by matrices, which for these nice equations would be overkill, I would find the inverse of 4 3 2 2 4 6 6 2 3 , then multiply that by...
October 15, 2014

Calculus I
or lim sin√x/e^x . clearly x≥0 use an intuitive approach. your numerator will be a number between -1 and 1, but your denominator keeps getting bigger and bigger so a relatively constant around ±1 divided by a huge number ---> 0 so lim x→ ∞ of ...
October 15, 2014

pre-calculus
This is very similar to the question you had before http://www.jiskha.com/display.cgi?id=1413245120
October 14, 2014

Math Check
for the 1st , I got -2 as the remainder for #2, did you mean (x^4 - 3x^2 + 2x - 1) / (x-1) ?? if so, then you are correct the way you had it would be one awful division.
October 14, 2014

math
if he spent 2/5 of it, then he has 3/5 of it left (3/5)x = 45 times 5 3x = 225 x = 75 His pocket money was $75
October 14, 2014

Geometry
Your symbols did not come out as you expected, but I concluded that you said: line BC bisects angle ABD, and angle ABC = 5x+11, angle CBD = 10x-4 so the two angles are equal, or 10x-4 = 5x+11 5x = 15 x = 3 check: angle ABC = 5(3) + 11 = 26 angle CBD = 10(3) - 4 = 26 YUP!!!
October 14, 2014

math
let sarah's sales be x then semir sold 3x and sung sold x+2
October 14, 2014

Math
cost of 3 pairs of shoes ---- x cost of handbag ---------- (1/2)x or x/2 x + x/2 = 324 times 2 2x + x = 648 3x = 648 x = 216 The 3 pairs of shoes cost $216 and the handbag cost $108
October 14, 2014

Math
ratio of games = 7x : 5x total games = 12x ration of games won : total games = 7x : 12x = 7:12
October 14, 2014

calculus
amount = 400(1/2)^(t/11.43), where t is number of days. so if t = 6 amount = 400(1/2)^(6/11.43) = 277.996 or appr 278 mg
October 14, 2014

math
done
October 14, 2014

math
1/2(x-2)<3/4(1-3x)<-2 preliminary: times 4 2(x-2) < 3(1-3x) < -8 2x - 4 < 3 - 3x < -8 2x-4 < 3-3x and 3 - 3x < -8 5x < 7 and -3x < -11 x < 7/5 and x > 11/3 no such number, thus no solution.
October 14, 2014

complex numbers
1. 4b-5t(-a-3)i=7-8i You don't say what you want. I see 3 variables in one equation, are you solving for one of them or what? 2. (7+4i) - (l+2i) is that supposed to say (7+4i) - (1+2i) ? then = 7+4i - 1 - 2i = 6 + 2i 3. (3+2i) (-2+4i) = -6 + 12i - 4i + 8i^2 = -6 + 8i - 8...
October 14, 2014

math prasad vk
1.2x = 2000 x = 2000/1.2 = .....
October 14, 2014

mathzzz preeshappd
Did you even look at how I did the same type of question for you just below ????
October 14, 2014

mathematiczzzzzz plzzzzzzzzzzzzzzz g
so manju spent 750 on the bike to make a profit of 15% on what she paid , she must sell it for 1.15(750) or 862.5 rupees
October 14, 2014

algebra
You did not define x I assume x represents the number of years since 1990 So for 1999 , x = 9 sub in 9 and evaluate YOur equation represents a parabola, find the vertex ... since the parabola opens up, there will be a minimum and a quick mental calculation will show that to be...
October 14, 2014

Math
1. "equilateral" means equal sides, but says nothing about its angles. How is regular defined ? 2. give yourself an example, e.g. consider a hexagon and an octogon, and see what happens 3. but the formula says 180(n-2) as the sum, so .... e.g. take a heptagon, n = 7...
October 14, 2014

maths
rate = distance/time = x km/20 min = 1000x m/1200 seconds = 5x/6 m/s
October 14, 2014

Math
1. let the number of sides be n each interior angle = 180(n-2)/n exterior angle = 360/n 180(n-2)/n = 3(360/n) + 20 times n 180(n-2) = 1080 + 20n 180n - 360 = 1080 + 20n 160n = 1440 n = 9 We have a 9-gon, which is called a enneagon or nonagon check: interior angle = 180(7)/9 = ...
October 14, 2014

maths
So you must select 3 or 4 women = C(8,3)*C(10,2) + C(8,4)*C(10,1) = 56(45) + 70(10) = 3220 check my arithmetic
October 14, 2014

math
assuming she went the same speed ... second trip/first trip = 4.75 rate/1.5 rate = 475/150 = 19/6 or appr 3.167 times as far
October 14, 2014

math
You could use Venn diagrams or use the formula: N(car OR cell OR married) = N(car) + N(cell)) + N(married) - N(car AND cell) - N(car AND married) - N(cell AND married) + N(car AND car AND married) =75+70+85-35 - 40 - 55 + 30 = 130 but there were 150 men considered, so 20 have ...
October 14, 2014

Finance
PV = 350(1.1)^-1 + 1000(1.1)^-3 + 1000(1.1)^-4 =
October 13, 2014

Math
both A and B are correct since they represent the same number 96 If the answer was supposed to be in scientific form, then B would be the correct choice, since the decimal must be after the first digit.
October 13, 2014

Math
hard to show in this format, since the numbers do not line up nicely 6 | 10 -50 0 0 -800 ...........60 60 360 2160 ..... 10 10 60 360 1360
October 13, 2014

math
case1 let a = .25, and b = .3 a+b = .55 which is < 1 case 2: let a = .8, and b = .7 then a+b = 1.5 which is NOT < 1 the statement should have been if a<1 and b< 1, then a+b < 2 (by adding the 2 inequalities)
October 13, 2014

Math
A, C, and D show a definite pattern of repetition, so they are rational B ??? hard to tell , perhaps there is a repetition further down I suspect the want you to say B
October 13, 2014

algebra
If the question was worded in that way, I would also have no clue .
October 13, 2014

Algebra
At 8:19 I posted this http://www.jiskha.com/display.cgi?id=1413243942 and showed you how to show exponents. You clearly did not even look at your previous post This question is the same type.
October 13, 2014

Math
scientific notation has a single digit number, followed by a decimal only A andB fit that property. look at the original number and compare it to A the decimal moved 8 places to the right, count them when you see 10^(negative) it represents a small number when you see 10^(...
October 13, 2014

Math
Did you count how many places the decimal point was moved? Then you must be sure of the answer.
October 13, 2014

Pre-Calc/Trig...
These are properties of a parabola that you absolutely MUST know to even be slightly successful in this topic. Giving you the answer will not help . Hint : make a quick sketch to see what the first one looks like for the second, why not sub in x = 0 as given in the point. Will...
October 13, 2014

math
treat the data as two ordered pairs, and find the linear equation (38, 2200) and (49,2125) slope = (2125-2200)/(49-38) = -75/11 so s - 2200 = (-75/11)(p-38) 11s - 24200 = -75p + 2850 11s + 75p = 27050 when s = 2143, 11(2143) + 75p = 27050 75p = 3477 p = $46.36 when s = 0 0 + ...
October 13, 2014

Calc: Related Rates
At a time of t seconds after noon, Jack will have walked 5t ft, while Jill will have walked 4t ft let the distance between them be d ft I see a right angled triangle with a base of 800-5t, a height of 4 t and a hypotenuse of d d^2 = (800-5t)^2 + (4t)^2 2d dd/dt = 2(800-5t)(-5...
October 13, 2014

Algebra
Use the following notation to show exponents x^2 - 4x - 19 = 13 x^2 - 4x - 32 = 0 (x-8)(x+4) = 0 take over.
October 13, 2014

inequalities
let's see when it IS 7 3x^3 + 4x^2 - 59x - 13 = 7 3x^3 + 4x^2 - 59x - 20 = 0 let's hope this factors nicely, tried: x = ±1, ±2, ±4, yup worked for x = 4 did synthetic division ... 3x^3 + 4x^2 - 59x - 20 = 0 (x-4)(3x^2 + 16x + 5) (x-4)(x+5)(3x + 1...
October 13, 2014

pre cal
if it does 2 rotations in 2 seconds, then it does 1 rotation in 1 second or 2π(13.5) inches per second = 2π(13.5)/12 ft /sec =7.06858.... ft/s (I stored in in my calculator memory for accuracy) = (7.06858...)/5280 miles / (1/3600) hr = appr 4.82 mph
October 13, 2014

Math
yes, according to the distance formula, the distance = √( (9-9)^2 + (-11 + 2)^2) = √(0 + 81) = √81 = 9
October 13, 2014

Calc
let the height of the balloon be h m then tanØ = h/60 , where Ø is the angle of elevation h = 60 tanØ dh/dt = sec^2 Ø dØ/dt when h = 30, dØ/dt = .1 rad/sec then tanØ = 30/60 = 1/2 hypotenuse = 30√5 secØ = 30√5...
October 13, 2014

typo - polar co ordinates
forgot the 4 in front of the 4cos^3 Ø should be x^2 + y^2 = 16x^3/(64r^3) - 3x/r x^2 + y^2 = (1/4)x/((x^2+y^2)√(x^2 + y^2)) - 3x/√(x^2+y^2)
October 13, 2014

polar co ordinates
the messy part is the cos (3Ø) we know cos 3Ø = 4cos^3 Ø - 3cosØ and since you know cosØ = x/r we get x^2 + y^2 = 16x^3/r^3 - 3x/r x^2 + y^2 = 16x/((x^2+y^2)√(x^2 + y^2)) - 3x/√(x^2+y^2) see: http://www.wolframalpha.com/input/?i=...
October 13, 2014

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