Sunday
February 14, 2016

Posts by Reiny

Total # Posts: 32,998

Math
I meant to say: ...according to some quadratic equation I would need 4 ordered pairs for a cubic. My work reflects what is needed for a quadratic
October 5, 2015

Math
ok George, I'll play your game. I will assume that the store owner is some math-nerd and sets the price of the numbers according to some cubic equation cost = ax^2 + bx + c, where x is the number of letters and a,b,c are constants so we have three ordered pairs: (1,40), (2...
October 5, 2015

Calc
since distance = rate x time d = 350t now look at your triangle. It is right-angled with a height of 1, a horizontal distance of d and the hypotenuse is s s^2 = 1^2 + d^2 , but d = 350t so.... s^2 = 1 + (350t)^2 s = √(1 + 122500t^2)
October 5, 2015

Scientific Notation
in scientific notation you start with a number between 1 and 10 followed by a decimal, multiplied by a power of 10 So 18 x 10^9 is mathematically correct it is not in scientific notation. the correct answer is 1.8 x 10^10 your 2nd question is correct
October 5, 2015

math statistic
I would have to know how many numbers I can pick from in Megabucks, you didn't say I will assume I can choose from 48 different numbers prob(win) = 1/48 prob(not win) = 47/48 so you want C(6,5)(1/48)^5 (47/48)^1 = .000000023 which is not the given answer. My answer is ...
October 5, 2015

AP Calculus AB
did you make your sketch? in my picture, I let the length of the person's shadow be y , and the distance of the person form the post as x as suggested. so by similar triangles, 5/y = 16/(x+y) 16y = 5x+5y 11y = 5x 11 dy/dt = 5 dx/dt dy/dt = (5/11)(2/x) = 10/(11x) this is ...
October 4, 2015

Math
I would use elimination, especially after looking at the y terms #3 - #2: x - 2z= 0 , so we already know z = 2y #1 times 2 : 8x - 2y + 4z = 22 original #2 as is: x + 2y - z = -1 add them: 9x + 3z = 21 or 3x + z = 7 double this: 6x + 2z = 14 using with : x - 2z = 0 add them 7x...
October 4, 2015

Calculus
product rule: g ' (x) = (5e^x)(1/2)x^(-1/2) + x^(1/2) (5e^x) clean it up any way you know how
October 4, 2015

Pre-Calculus
you started off the wrong way: the line joining your two points is not a tangent you want the tangent line at each of the given points, so there will be two different tangent equations. That is why it is so important to make a sketch. Let's just do one of them, for the ...
October 4, 2015

Calculus
g(Ø) = 16Ø - 4tanØ g ' (Ø) = 16 - 4sec^2 Ø = 0 4sec^2 Ø = 16 sec^2 Ø = 4 secØ = ±2 cosØ = ± 1/2 we know cos 60° or cos π/3 = 1/2 , and because of the ± , Ø could be in any ...
October 4, 2015

Pre-Calculus
Can you see how this question is the same as the one that Steve answered for you here ? http://www.jiskha.com/display.cgi?id=1443993008 Only the numbers have been changed to protect the innocent.
October 4, 2015

Pre-Calculus
let's put the sun at the origin and use x and y in units of 1 million so the orbit of Venus can be written appr a x^2 + y^2 = 67^2 then the comet is at (-73,80) which is clearly outside of the orbit of Venus. the most eastern point on Venus' orbit is (67,0) it might ...
October 4, 2015

Math
you must mean lim ( √(4+x) - 2)/x multiply top and bottom by √(4+x) + 2 lim ( √(4+x) - 2)/x = lim ( √(4+x) - 2)/x * (√(4+x) + 2)/(√(4+x) + 2) = lim (4+x - 4)/(x(√(4+x) + 2)) = lim x/(x(√(4+x) + 2)) = lim 1/(√(4+x) + 2) , as...
October 4, 2015

Algebra
a) http://www.wolframalpha.com/input/?i=h%3D-4.9t%5E2%2B29.4t%2B7 consider only the first quadrant b) just plug t = 5 and evaluate c) find the vertex of the parabola , and use the properties of the vertex. d) set 4.9t^2 - 29.4t - 7 = 0 and solve using the quadratic equation ...
October 4, 2015

math
prob(ontime) = .34 prob(not ontime) = (.66) more than 3 of 13 implies we CAN'T have 0 return + 1 return + 2 return + 3 return so prob(more than 3 return) = 1 - (sum of the 4 cases listed) I will do one of the 4 cases, you do the rest prob(3 of the 13 are returned) = C(13,3...
October 4, 2015

math
How many are NOT poor risk? divide that by 13838 , the total bonds round to 2 decimals (looks like we just have to follow the instructions)
October 4, 2015

math
double the 1st: 14x - 6y + 8z = 36 using the 2nd: 13x + 6y + 8z = 30 add them 27x + 16y = 66 , #4 triple the 1st: 21x - 9y + 12z = 54 using the 3rd: 11x - 9y - 12z = 16 subtract them: 10x + 24z = 38 5x + 12z = 19 , #5 #4 times 3 ---> 81x + 48y = 198 #5 times 4 ---> 20x...
October 4, 2015

math
all you have to do is put the math equations into words Sally's rate = house/4 , or use 1 to represent 1 house John's ratre = house/6 combined rate = house/4 + house/6 =(5house/12) time at combined rate = house/(5house/12) = house(12/5house) = 12/5 remember we could ...
October 4, 2015

Algebra
let the distance be d miles time against the wind = d/100 time with the wind = d/140 d/100 - d/140 = 1/4 times 700 7d - 5d = 175 d = 87.5 the two cities are 87.5 miles apart check time at slower speed = 87.5/100 = .875 hrs times at faster speed = 87.5/140 = .625 hrs difference...
October 4, 2015

algebra1
using your equation just the way you typed it .... multiply each term by -56 , the LCD -336 + 7x = 32 7x = 368 x = 368/7
October 3, 2015

math
Why could you not follow the same steps I showed you for the other questions in that same sequence, when you posted this before ? http://www.jiskha.com/display.cgi?id=1443837328 show me your steps.
October 3, 2015

math
total area = (8 2/5)(18 1/3) ft^2 = (42/5)(55/3) = 154 ft^2 now take 1/2 of that
October 3, 2015

Integration need help also
we know that cos 2x = 1 - 2sin^2 x 2sin^2 x = 1 - cos 2x sin^2 x = 1/2 - (1/2)cos(2x) so integral(sin^2 x)dx = integral( 1/2 - (1/2)cos(2x) ) dx = (1/2)x - (1/4)sin(2x) + costant
October 3, 2015

Integration need help
Using the "Just look at it Theorem" Integral (6x^2 - cos(2x) dx = 2x^3 - (1/2)sin(2x) + constant you can easily check by mentally finding the derivative of the above answer
October 3, 2015

Prove that sin(A+B) need help
or look at this video, very simple explanation: https://www.youtube.com/watch?v=4K6xr8hjkTw
October 3, 2015

Digits in number**
number of cases: (X is any digit except 6) 6XX = 9X9 = 81 X6X = 8x9 = 72 , can't have 0 at the front XX6 = 8x9 = 72 66X = 9 6X6 = 9 X66 = 8 Number of cases = add them up
October 2, 2015

Math
ahhh, did not see your reply last night, had gone to bed so it was: |(4/5)n + 9/2| = 49/10 then (4/5)n + 9/2 = 49/10 OR (-4/5)n - 9/2 = 49/10 I had solved the first version of that and got n = 1/2 solve the second equation to get the second solution. since n = 1/2 shows up ...
October 2, 2015

Math
(4/5)n = 49/10 - 9/2 (4/5)n = 2/5 4n = 2 n = 1/2
October 2, 2015

math
#1, #2 ok #3 your connective should be OR how can a number be 12 and -28/3 #4 5|2x + 1 | = 55 |2x + 1 | = 11 2x+1 = 11 OR -2x-1 = 11 2x = 10 or -2x = 12 x = 5 or x = -6 5. Solve: 1/2|4x – 8| - 7 = 3 5. Solve: 1/2|4x – 8| = 10 5. Solve: |4x – 8| = 20 4x-8 = 20 or...
October 2, 2015

Geometry
The volume of similar 3-D solids is proportional to the cube of their corresponding sides, so V/144 = 4^3/3^3 V = 144(64/27) = appr 341.33 in^3 or original: 144 = 3lh lh = 144/3 new: increased by a factor of 4/3 width = 4 length = (4/3)l height = (4/3)h new volume = 4(4/3l)(4/...
October 2, 2015

Algebra 2
(x+1)(x+8) expand using the distributive property, collect like terms
October 2, 2015

Math word problems
number of cheaper sets ---x number of other sets ----- 200-x 15x + 45(200-x) = 5700 solve for x
October 2, 2015

math
3 of the 20 L barrels = 3(20000) ml = 60000 ml at a rate of 100 ml/s it would take 60000/100 seconds = ...
October 2, 2015

HELP PLZ WITH MATH
I see you retyped your question , (see your previous post of this) but 8–^2 still makes no sense
October 2, 2015

math
radius must be 115 ft and its center must be 245-115 or 130 above the x-axis, (the ground) equation: x^2 + (y-130)^2 = 115^2 = 13225 see http://www.wolframalpha.com/input/?i=x%5E2+%2B+%28y-130%29%5E2+%3D+13225
October 2, 2015

Geometry
So you want 2/3 of one cone volume = (2/3)(1/3)π(3^2)(12) = 24π cm^3
October 2, 2015

Math
I am guessing you have a typo and you meant: (8^-2)(40) then = (1/64)(40) = 40/64 = 5/8 , Collins had that also so I guess that is not what you meant after all. retype the problem using correct notation.
October 2, 2015

Geometry
did you mean (x+5)^2 + (y+3)^2 = 169 ? then the centre would be (-5,-3) and the radius , (or the range) , would be 13 http://www.wolframalpha.com/input/?i=%28x%2B5%29%5E2+%2B+%28y%2B3%29%5E2+%3D+169
October 2, 2015

I need help maths jus so confused
Newton's Method perhaps? x^x = 100 take ln of both sides, and use log rules xlnx = ln100 let y = f(x) = xlnx - ln100 dy/dx = x(1/x) + lnx + 0 = 1 + lnx Newton is effect said: newx = oldx - f(oldx)/f ' (oldx) , using x for oldx = x - (xlnx - ln100)/(1+lnx) = (x + xlnx...
October 2, 2015

math
ummh, wouldn't that just be 200/15 m/s = 40/3 m/s
October 2, 2015

Math
students --- 17x faculty ----- 3x 17x+3x = 740 carry on
October 2, 2015

Grrrhhhh _ Foley
Thanks Steve. I just have to read those questions more carefully
October 2, 2015

Foley
angle3 = 126° then angle2 = 54°, since angle2 + angle3 = 180° then angle1 = 126°, since angle2 + angle1 =180°
October 2, 2015

investment
Looks like your text is at least 7 years old http://www.jiskha.com/display.cgi?id=1200017478
October 2, 2015

mathematics
right now: boys --- x girls --- x+5 2 boys join class: boys = x+2 girls = x+5 (x+2)/(x+5) = 5/4 solve for x , sub into x+5
October 2, 2015

Logarithm prove abc
remember that we can switch bases of logs using the property that logq p = log p /log q , where p,q > 0 and the logp/loq has the same base. So I will choose base 10, that way I don't have to write the base then abc = (log2x x)(log3x 2x)(log4x 3x) abc = (log x/log 2x)(...
October 2, 2015

Math
time after lunch --- t minutes before lunch = 5t - 1 t + 5t-1 = 41 solve for t
October 2, 2015

maths
speed of A --- 2x units/min speed of B --- 3x time for trip for A = trip/2x = t/2x, where t is the trip time for trip for B = trip/3x = t/3x t/2x = t/ 3x + 10 t/(2x) - t(3x) = 10 times 6x 3t - 2t = 60x t = 60x case2: speed of A = 6x speed of B = 3x/2 time for A = t/(6x) time ...
October 2, 2015

Probablity
This page will replace any tables or charts in the back of texts or handouts you might have been given http://davidmlane.com/hyperstat/z_table.html enter: mean -- 400 SD -- 45 click on "above" and enter 470 prob is .0599 ---> 5.99% ii) click on "between"...
October 1, 2015

Uclm
let the left page be numbered n then the right page is n+1 n + n+1 = 193 solve for n
October 1, 2015

Algebra
I hope you weren't just guessing. 1. 3p + 3q = p 2p = -3q p = -3q/2 The way you typed the answers, none are valid 2. d = rt d/t = r , all you have to do is divide both sides by t 3. 2L + 2W = P 30 + 2W = 90 2W = 60 W = 30 0 for 3 , looks like somebody has some work ahead
October 1, 2015

Sphere find x
I don't think Steve is on line right now, so ... look at his 1.728v = (1 + .728)v = (100% + 72.8%)v , since 100% = 100/100 = 1 can you see where it came from?
October 1, 2015

Probability license Arrangements
Found a typo .... forgot the = sign should be : All cases = 7 x 36 x 36 x 10 x 10 = 907200
September 30, 2015

Probability license Arrangements
so a possible valid choice could be R 2S 56 All cases = 7 x 36 x 36 x 10 x 10907200 Assuming 5 vowels number of cases without a vowel = 4 x 31 x 31 x 10 x 10 = 3844400 prob(of having a vowel) = 1 - 384400/1090700 = appr .576 check my arithmetic
September 30, 2015

math
when 2/3 of a pound costs $2.50 you are saying that 1 pounds costs less than a penny??? really??? if 2/3 pounds costs 2.50 then 1 pound costs 2.5/(2/3) = $3.75
September 30, 2015

algebra 2
looks like the y's would be the first line of attack add 1st and last ----> 8x + 6z = 44 4x + 3z = 22 double the first ---> 6x + 2y + 2z = 28 keep second as is --> -x + 2y - 3z = -9 subtract them: 7x + 5z = 37 4x + 3z = 22 --times 5 --> 20x + 15z = 110 7x + 5z...
September 30, 2015

math
your method is ok, must be in the execution. show your steps so I tell where you went wrong
September 30, 2015

Probability
10 different horses can come in 1st then 9 different horses come in 2nd, and then 8 different horse come in 3rd so number of ways = 10(9)(8) = 720 btw, 10!/7! = 10*9*8*7!/7! = 10*9*8 = 720, which was your answer, so you are right
September 30, 2015

Math
1. f(x) = ((1/108)x^6)(6lnx - 1) product rule: f ' (x) = (1/108)x^6 (6/x) + (1/18)x^5 (6lnx - 1) = (1/18)x^5 + (1/18)x^5)(6lnx - 1) common factor of (1/18)x^5 = (1/18)x^5 (1 + 6lnx - 1) = (1/3) x^5 lnx check: http://www.wolframalpha.com/input/?i=derivative+%28%281%2F108%...
September 30, 2015

math
The two examples you have are pretty straight-forward. You will just have to practise and practise until you can do those. I will do #6 10 < (20-9.8t) < 20 subtract 20 from each part -10 < -9.8t < 0 divide each part by -9.8, remember to reverse the inequality sign ...
September 30, 2015

Norman
larger --- x smaller ---- y x-y = 4 ----> x = y+4 3y - x = 10 sub in the first: 3y - (y+4) = 10 3y - y - 4= 10 2y = 14 y = 7 then x=7+4 = 11 the larger is 11 , the smaller is 7 check: their difference is 4 , check! 3 times the smaller minus the larger is 10 21 = 11 = 10 , ...
September 30, 2015

geometry
see previous post
September 30, 2015

geometry
D = √((-2-1)^2 + (4-3)^2 ) = ...
September 30, 2015

Algebra/Math
done http://www.jiskha.com/display.cgi?id=1443624663
September 30, 2015

math
nope, think about what it means ... y^4 = yyyy y^3 = yyy so (y^4)(y^3) = (yyyy)(yyy) = y^7 when multiplying powers with the same base, keep the base and add the exponents
September 30, 2015

Equation find x xo tricky
I read that as: (x^x)√x = x(√x^x) square both sides x^(2x)(x) = x^2(x^x) x^(2x+1) = x^(x+2) 2x + 1 = x+2 x = 1
September 30, 2015

Math Answer Check
1. ok #2 why are you giving the negative result? cos 7π/2 = 0 so we need cos^-1 (0) = π/2 see: http://www.wolframalpha.com/input/?i=arccos%28cos%287pi%2F2%29%29+ #4. arctan (11/60) construct a right-angled triangle with opposite as 60 and adjacent as 11 r^2 = 11^2 + ...
September 30, 2015

Washington high
part at 10% --- x part at 7% = 12000 - x solve for x .1x + .07(12000-x) = 960
September 30, 2015

math
A = { 3, √2, 2√3, √9, √7} , but √9 = 3 which is rational, so you have 2 rationals out of the 5 well ?
September 30, 2015

correction - maths
(-5 i)(1/8 i) = (-5/8) i^2 , but i^2 = -1 = 5/8
September 30, 2015

Math
I will number your problems 1. ok 2. you need 6.5 ÷ 1/3 = 19.5 I would have expected a whole number, since it deals with people. So 19 would receive a full 1/3 of a box, and the 20th person would get less than 1/3 of a box 3. 3^2 = 9 , which is rational 1/5 is rational ...
September 30, 2015

math
don't you get a right-angled triangles with legs of 30 and 60 ? How about Pythagoras ?
September 30, 2015

math
tile : board = 1/3 ft : 1/2 yds = 4 inches : 18 inches = 2 : 9 area of tile : area of board = 2^2 : 9^2 = 4 : 81
September 30, 2015

TC Maths
recall that sinxcosx - sinycosy = cos(x+y) LS = (sin^2(x)-cos^2(y))/(Sinx cosx-Sinycosy) notice I inserted the absolutely necessary brackets to make the statement true = (sinx + cosy)(sinx - cosy)/(cos(x+y)) not getting anywhere ≠ tan(x+y) I usually test the equation ...
September 30, 2015

Word problem maths
Restating what Steve said in a slightly different way: sum of ages of all 21 boys = 21(14 3/12) = 299 1/4 sum of ages without oldest = 20(14 2/12) = 283 1/3 age of boy not included (oldest) = 299 1/4 - 283 1/3 = 15 11/12 which is exactly what Steve did
September 30, 2015

Calculus
well, let's set the velocity equal to zero ... 3t^2 - 12 = 0 3t^2 = 12 t^2 = 4 t = ± 2, but t ≥0 so the velocity is zero when t = 2 so what is the acceleration when t = 2 ??
September 29, 2015

Algebra I
Your text or notes should have definitions for a relation and a function In simple terms, a relation is any equation that contains two different variables, usually x's and y's e.g. x + y = 8 is a relation again, in simple terms, if I can isolate the y so it is ...
September 29, 2015

Calculus 1
well, there you go, how about that
September 29, 2015

Calculus 1
First of all -9/2x-5/2 is NOT an equation if you meant y = -(9/2)x - 5/2 then by golly, that is what my equation is 9x + 2y = -5 2y = -9x - 5 divide each term by 2 y = (-9/2)x - 5/2 My answer is correct.
September 29, 2015

Calculus 1
y^2=5x^4-x^2 2y dy/dx = 20x^3 - 2x dy/dx = (20x^3 - 2x)/(2y) = (10x^3 - x)/y at (-1,2) dy/dx = (-10+1)/2 = -9/2 so the tangent equation is 9x + 2y = c with (-1,2) lying on it, so -9 + 4 = c = -5 the tangent equation is 9x + 2y = -5 check: http://www.wolframalpha.com/input/?i=y...
September 29, 2015

Calculus 1
If it is an astroid, then it should be x^(2/3) +y^(2/3) =4 the way you typed it would result in a circle http://www.wolframalpha.com/input/?i=x%5E2%2F3+%2By%5E2%2F3+%3D4 (2/3)x^(-1/3) + (2/3)y^(-1/3) dy/dx = 0 x^(-1/3) + y^(-1/3) dy/dx = 0 dy/dx = -(x^(-1/3))/y^(-1/3) = -(x/y...
September 29, 2015

math
Question looks incomplete, but I think I can figure out what you want. Joel's speed --- x Kyle's speed --- x+10 6x + 6(x+10) = 780 solve for x and you got it
September 29, 2015

Indices
What is all this nonsense? Notice all 3 powers can be expressed as a power with base 2, thus as a power with base 4 P = (64)^-2 = (4^3)^-2 = 4^-6 Q = (1/16)^(1/3) = 16^(-1/3) = (4^2)^-1/3) = 4^(-2/3) R = 8√2 = 2^3(2^(1/2)) = 2^(7/2) = (4^(1/2))^(7/2) = 4^(7/4) the PQR...
September 29, 2015

algebra
first equation: 2x - 5y = 8 double the 2nd: 2x - 6y = -2 subtract them: y = 10 back into the original 2nd x - 3y = -1 x - 30 = -1 x = 29 x = 29, y = 10
September 28, 2015

Math
The hundred thousands digit is more than six XX7XX XX8XX XX9XX The thousands digit can be divided by the ones digit and since the number is even, the ones digit is even X47X2 X87X4 X48X2 X88X2 , but all digits are different, so skip the last, so X48X2 X49X2 X89X4 The ten ...
September 28, 2015

math
Place Shane in the first chair, then the remaining 5 students can be arranged in the 5 chairs in 5! or 120 ways
September 28, 2015

algebra
anything^0 = 1 , as long as you don't have 0^0
September 28, 2015

Math
base will be 8-2x by 6-2x height = x volume = x(8-2x)(6-2x) = 192 , where x<3 x(48 - 28x + 4x^2 = 192 4x^3 - 28x^2 + 48x - 192 = 0 x^3 - 7x^2 + 12x - 48 = 0 tried all the "nice" factors of 48, and found no solution. So I let Wolfram graph it and solve it to ge x...
September 28, 2015

math
see earlier post of the same question
September 28, 2015

math
increase in the length from 8 to 10 is 2cm percent increase = 2/8 = 25% old area = 40 new area = 70 increase = 30 percent increase = 30/40 = 75% did you realize that the increase will result in a distortion ? The percentage increase of the length is NOT the same as the ...
September 28, 2015

calculus
1. An amplitude of 1 applies to only the sine or cosine function. the given domain puts the angle in the 2nd quadrant. in that quad, the sine is positive and the cosine is negative, so it has to be y = cosx 2. I know that sin30° = sin(π/6) = 1/2 so csc (π/6) = 2 ...
September 28, 2015

precalc
there are 3 pairs of cofunctions sine vs cosine tangent vs cotangent secant vs cosecant Surely your text or notes have definitions of the reciprocal functions.
September 28, 2015

Math
Let's play "I spy" I spy with my little eyes two equal numbers sitting side by side.
September 28, 2015

math
Damon did this earlier today http://www.jiskha.com/display.cgi?id=1443455187
September 28, 2015

Math
In 5 hrs the first train went 5(68) or 340 km in the same 5 hrs, the 2nd train went 310 km So what do you think?
September 28, 2015

Math(ANSWERCHECK)!!
I got 7.159 but perhaps your skills of button-pushing are better than mine
September 28, 2015

MathHELP!
g(x) factors very nicely to g(x) = (x+1)^2 suppose you write it as g(x) = (x+1)^2 + 0 and you compare it to f(x) = a(x-h)^2 + k, which you must have learned and studied to do this topic
September 28, 2015

math
since there is a repeat of 117 in the decimal, it is rational. take 117/999 on your calculator your second answer of 32/100 is not in lowest terms as asked for 32/100 = 8/25
September 28, 2015

math
9. r = d/t multiply each side by t ---> d = rt 10. 3x - y = 10 add y to both sides 3x = y + 10 subtract 10 form both sides 3x - 10 = y strange way of doing equations: here is how I would do the last e.g. P = 2l + 2w P - 2l = 2W -----> I subtracted 2l from both sides P/2...
September 28, 2015

Math Help
What makes you think so ?
September 28, 2015

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