Wednesday
September 3, 2014

Posts by Reiny


Total # Posts: 27,024

math
I like that equation. What about it ?
February 26, 2014

Algebra
5x^2 - 526 = -651 5x^2 = -125 x^2 = -25 Unless you have another typo, there is no real number solution, since we cannot take the square root of a negative. If you equation was supposed to be 5x^2 - 526x= -651 5x^2 - 526x + 651 = 0 x = (526 ± √263656)/10 = appr 103...
February 26, 2014

Math
If my middle term is even and it starts with x^2, I always complete the square. x^2 + 14x + 49 = -4 + 49 (x+7)^2 = 40 x+7 = ± √40 = ± 2√10 x = -7 ± 2√10
February 25, 2014

Math
Use the formula exact values: x = (5 ± √13)/2 Use your calculator to find appr. values
February 25, 2014

Finance
PV = 235 (1 - 1.006458333..^-48)/.006458333 = $ 9672.48
February 25, 2014

Maths
A - B = 51 ---> A = B+51 A - C = 108 subtract them -C + B = 57 B = C + 57 C = (15/100)(A+B+C) C = (3A + 3B + 3C)/20 20C = 3A + 3B + 3C 17C = 3A+ 3B 17C = 3(B+51) + 3(C+57) 17C = 3B + 153 + 3C + 171 17C = 3(C+57) + 153 + 3C + 171 17C = 3C + 171 + 153 + 3C + 171 11C = 495 C...
February 25, 2014

Geometry A
The line y+4 = 3(x+6) does expand and simplify it if you have to
February 25, 2014

algebra
8| x+3/4|< 2 | x+3/4| < 1/4 x+3/4 < 1/4 AND -x-3/4 < 1/4 x < -1/2 AND -x < 1 x < -1/2 AND x > -1 which matches: -1 < x < -1/2
February 25, 2014

algebra
2|3 x-5|-8=8 2|3 x-5| = 16 |3 x-5| = 8 3x-5 = 8 or -3x+5 = 8 3x = 13 or -3x = 3 x = 13/3 OR x = -1 choose your matching answer, it is there.
February 25, 2014

Math
welcome
February 25, 2014

Math
distance = √( (5-1)^2 + (-4+2)^2 ) = √(16 + 4) = √20 = appr 4.47 I would leave it in exact form of √20 or 2√5
February 25, 2014

algebra
2(8x-4)-2 x<14x+12 16x - 8 - 2x < 14x + 12 -8 < 12 which is a true statement, thus your inequation is true for all values of x so always
February 25, 2014

algebra
solve it to see which choice is correct
February 25, 2014

algebra
2(8 x-4)-<14 x+12 16 x - 8 ≤ 14x + 12 2x ≤ 20 x ≤ 10 what do you think?
February 25, 2014

algebra 1
let the number of 4-people cars be x then the number of 6-person cars is 15-x 4x + 6(15-x) = 72 4x + 90 - 6x = 72 -2x = -18 x = 9 9 of the 4-person cars and 6 of the 6-person cars
February 25, 2014

Math
These non-metric units always confuse me, so since I use metric most of the time, I will convert to decimals consider 1 board + 1 gap to be one unit so we have 6.5 + .1875 = 6.6875 inches 6.5 = .25 = 6.75 6.5 + .375 = 6.875 now... 18 feet = 216 216/6.6875 = 2.6932.299.. 216/6....
February 25, 2014

Math
arggh, just a lot of arithmetic..... time per day open for rides: 6.5 hours = 390 minutes time available per year = 390(365) = 142350 minutes time needed to complete one ride = 3 + 4 + 3 = 10 minutes. (so they can complete 39 rides per day) number of rides per year = 142350/10...
February 25, 2014

Math
look at the pattern 1 line --- 0 intersection 2 ines --- 1 intersection 3 lines ---- 3 intersections 4 lines ---- 6 intersections 5 lines --- 10 intersections 6 lines ---- 15 intersections ..... the numbers of the sequence 1 3 6 10 15 .... are called the "triangular ...
February 25, 2014

maths
2nd term = a+d 6th term = a + 5d "the 6th term is 3 times the second term" --> a+5d = 3(a+d) a+5d = 3a + 3d 2d = 2a a = d "the 5th term is 15" ---> a+4d = 15 but a = d 5d = 15 d = 3 then a = 3 "the 4th term is 4 times the first term" --> ...
February 25, 2014

Algebra
or 100x/(x+314) = 42 cross-multiply ... 100x = 42x = 13188 58x = 13188 x = 13188/58 = 6594/29 or appr 227.38 I took your * to mean multiplication, the common symbol for multiplication If, somehow, you meant it to be an exponent, that is [x/(x+314)]^100 = 42 then take the 100th...
February 25, 2014

German Help Please....
#1 , ok #2, should be Sie haben den Film lieber. You need the plural, your choice would say "She prefers the film" , which would be singular #3 choice D, yours sounds like a Google translation #4 ok #5 A, B, and C are definitely out, C sounds very clumsy, I would say...
February 25, 2014

Math
cost = 50 + 2n, where n is the number of pages if n = 75 Cost = 50 + 2(75) = ....
February 24, 2014

Calculus
Just about every Calculus book I have ever seen uses this question as an introductory example of "rate of change" problem. At a time of t seconds, let the foot of the ladder be x ft from the wall, and the top of the ladder by y ft above the ground> then, x^2 + y^2...
February 24, 2014

math
sorry about the typo, but I am sure you were able to make sense out of it.
February 24, 2014

math
I am assumungthere are 26 lower case, 26 upper case and 10 digits that can fill any position number of all possible cases = 62^6 = 5.68 x 10^10 (huge) number without any digits = 52^6 = 1.977 x 10^10 (still huge) so the number of possible cases with at least 1 digit = number ...
February 24, 2014

math
lower end speed: so far --- time = 70/50 = 1.4 hrs total trip -- time = 154/50 = 3.08 hrs top end speed: so far --- time = 70/57 = 1.23 hrs total trip -- time = 154/57 = 2.701 hrs I don't see a " which of the following" part , so use my results above to match ...
February 24, 2014

math
to go from 1: 15 to 1:16 the minute hand has moved (1/60)(360)° or 6° but the hour hand has also moved (1/60)(1/60)(360)° or 1/10 ° so the change in angle is 6 - 1/10 ° or 59/10 ° or 5.9°
February 24, 2014

algebra
On my screen the - was on one line and the 2(.... on the next, so I read it as shown if your statement was -2(2x+9) > -4x + 9 your x's would drop out and you have the situation when you posted as "Lucky". Draw your conclusion.
February 23, 2014

algebra
4x + 18 > -4x + 9 8x > -9 x > -9/8 which of your answers matches this ?
February 23, 2014

algebra
26+6b > 2(3b+4) 26 + 6b > 6b + 8 26 > 8 , which is true so it is true for all real values of b
February 23, 2014

math
Did you notice one parabola opens up, the other one down To have only one point of intersection, they must have a common tangent, that is the slope of one equals the slope of the other for the 1st: dy/dx = 2x+6 for the 2nd dy/dx = -2x - 6 2x + 16 = -2x -6 4x = 12 x = 3 when x...
February 23, 2014

algebra
What is 5(-6) + 5(-5) ?
February 23, 2014

math
mmmh, they gave you the equation y = kx^2 when y = 50, x = 10 , so.... 50 = k(100) k = 1/2 your equation is y = (1/2)x^2 now just plug in x = 30 in your head you can do y = 900/2 or 450
February 23, 2014

math
complete the square to find the centre x^2 -10x + 25 + y^2 = k + 25 (x-5)^2 + y^2= k+25 so the centre must be (5,0), which lies on the x-axis to be tangent to the y-axis it must pass through (0.0) and its radius must be 5 so the equation must be (x-5)^2 + y^2 = 25 and k+25 ...
February 23, 2014

Math
isn't profit = revenue - cost ? plug in those values, simplify, then use either of the methods I just showed you in your previous post
February 23, 2014

Math
So in effect you are finding the vertex of the downwards opening parabola shortest way: the x of the vertex is -b/(2a) = -8/-.8 = 10 when x = 10 N(10) = -.4(100) + 8(10)+11 = 51 The ticket sales will peak at day 10 and on that day 51 tickets are sold method 2: complete the ...
February 23, 2014

business finance
so you are financing 55000 - 15000, or 40000 so let the monthly rate be i 1050(1 - (1+i)^-60)/i = 40000 payment = 40000/( 1 - (1+i)^-60)/i checking for some interest rates let i = 0, (no interest) payment = 40000/60 = 666.67 let i = .005 , (6% interest) payment = 40000/ (1 - 1...
February 23, 2014

maths
Ohh dear! midpoint is a "point" so it must look like ( ? , ? ) your method should be the x of the midpoint is (6+0)/2= 3 the y of the midpoint is (6-2)/2 = 2 so the midpoint is (3,2) (notice that in effect we are taking the average of the x's and the average of ...
February 23, 2014

maths
gradient = slope = (6-(-2))/(6-0) = 8/6 = 4/3 since (0,-2) is the y-intercept or the b of the y = mx + b notation, we can simply write y = (4/3) - 2 surely you have 2 little formulas in your text or your notebook to find the midpoint and the length. Let me know what you get.
February 23, 2014

Math
y = 4x^2 + 1 dy/dt = 8x dx/dt when x = 2, dy/dt = 1/2 sub that in.... 1/2 = 16 dx/dt dx/dt = 1/32
February 23, 2014

Precalculus
I was the one that answered you before when you had the typo (you had S instead of A for the short-tailed mice) and I actually found my scrap piece of paper where I made my Venn diagram. so.... My Venns agree with your data, and n(M' union S) = n(non male) + n(short tailed...
February 23, 2014

Math
I am going to assume that the kitchen and the dining room have the same width. so the length of large rectangle is x+12 and the width is x so x(x+12) = 589 x^2 + 12x = 589 x^2 + 12x + 36 = 589+36 (x+6)^2 = 625 x+6 = ± √625 = ± 25 x = -6 + 25 or -6-25 , the ...
February 23, 2014

math
put the decimal between the 1 and 4, then count the number of decimals it was moved from the end of the big number = 1.406 x 10^?? , you do the counting.
February 23, 2014

math class
f '(3) = 4 says that the slope is 4 when x = 3 f)3) = 9 means that you are dealing with the point (3,9) So they have given you the slope of the line and a point on it. I am sure you can take it from there.
February 23, 2014

calculus
What about it ?
February 23, 2014

Math
let x^2 - 18x - 4 = 0 best done by completing the square x^2 - 18x + 91 = 4 + 81 (x-9)^2= 85 x - 9 = √85 x = 9 ± √85 Your question should have said "What are the zeros of ...." , since there are two of them.
February 23, 2014

math class
The derivative should have been dy/dx = -3x^-4 = -3/x^4 when x = .5 or 1/2 dy/dx = -3/(1/2)^4 = -3/(1/16 = -3(16) = -48
February 23, 2014

math
first day he ran 1.5 2nd day he ran 1.5(1.1) 3rd day he ran 1.5(1.1)(1.1) = 1.5(1.1)^2 .. on the 7th day he ran 1.5(1.1)^6 so we have: 1.5 + 1.5(1.1)+ 1.5(1.1^2 + ... + 1.5(1.1)^6 which is a geometric series whose sum is 1.5( 1.1^7 - 1)/(1.1 - 1) = 1.5(.9487171)/.1 = 14....
February 22, 2014

Pre-calculus
your equation "falls apart" when p = 100 because you would be dividing by zero So mathematically, the cost would be infinitely large (that is, it is not possible) look at this graph and see what happens at p = 100 http://www.wolframalpha.com/input/?i=plot+C%3D80%...
February 21, 2014

not Calculus Please help!
B) compounded quarterly ----> i = .07/4 or .0175, and n = 6(4) or 24 amount = 7000(1.0175)^24 = $ 10,615.10 Do A and C the same way D amount = 7000 e^(6(.07)) = $ 10,653.73
February 21, 2014

Calculus Please help!
-8x + 4x dy/dx + 4y - 6y^2 dy/dx = 0 dy/dx(4x - 6y^2) = 8x - 4y dy/dx = (4x - 2y)/(2x - 3y^2) plug in x = 1 and y = 3 to find the slope
February 21, 2014

Math
Let the dimensions of the box by x by y by z xyz = 80 z = 80/(xy) "least amount of plasic" implies least surface area SA = 2xy + 2xz + 2yz = 2xy + 2x(80/(xy)) + 2y(80/(xy)) = 2xy + 160/y + 160/x now we know that xyz = 80 and 80 = (2)(2)(2)(2)(5) combinations of x y z...
February 21, 2014

Math
For simplicity sake, let's assume that the temperature increase is a linear function, (which it isn't), we would solve 2t + 20 = 98 2t = 78 t = 39 seconds
February 21, 2014

Math! HELP!
(3/2b^4)^3 = (27/8)b^12 (3/5y^4)^-2 = 1/(3/5y^4)^2 = 1/( (9/25)y^8 = 25/(9y^8) or (25/9)y^-8
February 21, 2014

Algebra 1
5x^2 + 2x^2 = 7x^2 (5 apples + 2 apples = 7 apples) Steve had a typo, happens even to the best of us
February 21, 2014

Algebra 1
Your question was answered , go back and check
February 21, 2014

Intermediate algebra
let number of AC adapters be x let number of flashlights be y 7x + 2y = 86 3x + 4y = 84 double the first equation 14x + 4y = 172 3x + 4y = 84 subtract them 11x = 88 x = 8 sub back into 1st: 7(8) + 2y = 86 2y = 30 y = 15 so 8 adapters and 15 flashlights. Check my answer to see ...
February 21, 2014

Algebra 1 Answer Check
1. correct if you meant 49^(3/2) The way you typed it --- 117649/2 2. can't read the question 3. the leading term in standard notation would be 8x^2 so leading coefficient is 8 4. correct 5. the x is undefined in your problem 6. 7x^2 - 2x + 5, the exponent is not affected ...
February 21, 2014

algebra
Steve is right, go with x-8 ≥ 20
February 21, 2014

algebra
After trying to make sense of your garbled English, I would pick x-8 > 20
February 21, 2014

algebra
Visualize the candy cane made in the form of a paper cylinder. Cut the cylinder open, you will see that the "ribbon" around the candy cane or cylinder consists of 4 diagonals for 4 different rectangles. the height of each of those rectangles is 20/4 or 5 cm and the ...
February 21, 2014

math help
poorly written up you lost the ratio notation and lack the equal sign correct presentation: 18 : 0.6 = 180 : 6 = 30 : 1
February 20, 2014

Math
I suspect you mean (x+1)/(x-2) = 3/6 confirm before I proceed
February 20, 2014

Algebra
the first one is already factored, so how come you are stuck on it ? 2nd: get the equation = 0 then it factors quite easily 4a^2 - 11a + 6 = 0 and 9r^r - 30r + 21 = -4 have you not been taught some kind of a method to factor these kind of trinomials? A common method these days...
February 20, 2014

Probability
I will assume that you filled in the Venn diagrams correctly n(M upside down u W) ---> n(M and W) = 14 n(M' U S) ---> n(M' or S) Since S is the symbol used for the universal set, the count would be 49 P( both mice are short-tailed) --- where does the "both&...
February 20, 2014

Algebra
Yeahhh! you got it
February 20, 2014

Algebra
4x^2 - 8x - 12 + 6x , looks like grouping works nicely = 4x^2- 8x+ 6x - 12 = 4x(x-2) + 6(x-2) = (x-2)(4x+6) = 2(x-2)(2x+3) 144 - 9p^2 , should have recognized difference of squares = (12-3p)(12+3kp) 5c^2 - 24cd - 5d^2 if it factors it must start with (5c ...)(c...) and end ...
February 20, 2014

Algebra 1 (Reiny)
Perimeter = 2s^3+4 + 5s + 4s^2 + 1 = 2s^3 + 4s^2 + 5s + 5 Why was this question difficult for you? If you are given the three sides of a triangle, wouldn't you just add them up to find the perimeter ?
February 20, 2014

Math
6x-2 = 3x+1 OR 6x-2 = -3x - 1 3x= 3 OR 9x = 1 x = 1 OR x = 1/9
February 20, 2014

Math
Mandy ---- b jay ------- b-3 kareem --- 2b look at my definitions,
February 20, 2014

Algebra
#1 should be -3x^2 + 5x- 12 #2 3x^2+ 5x - 6x - 10 = 3x^2- x - 10 #3, good, yeahhh #4, -2p^2 + 27p #5, yeahhh #6 good grief!!! = 2m^3 + 4m^2 + 8m - 4m^2 - 8m - 16 = 2m^3 - 16 #7, correct
February 20, 2014

math
let f(x) = ax^4 + bx^2 + c f(-1) = 0 , since it is a factor but f(-1) = a+ b + c so a+b+c = 0
February 20, 2014

advanced functions
-2t^3+3t^2+149t+410 = 980 2t^3 - 3t^2 - 149t + 570 = 0 could try 1, 2, 3, 4, 5 ,6, 7, 8, 9 ,10 Well, what do you know, t=5 works and so does t = 6 so there has to be 3 factors, I know the first two are (t-5)(t-6)(? t + ?) = 0 by the "common sense" theorem, the third ...
February 20, 2014

Algebra
see http://www.jiskha.com/display.cgi?id=1392932194
February 20, 2014

Algebra
If you meant y = -7/(x-16), then the domain is any real number, x ≠ 16 and for every x you pick there is one and only one value of y , except x=16 so it is a function.
February 20, 2014

Algebra
5y = 2x + 9 y = (2/5)x + 9/5 or y = (2x + 9)/5 now write f(x) = ... either of the two versions, both are correct
February 20, 2014

Math Algebra
Nice, that's the way I would do it,
February 20, 2014

Algebra
1/A + 1/B + 1/C = 3400 , #1 1/A + 1/B = 1900 (A+B)/(AB) = 1900 1900AB = A+B 1900AB - B = A B(1900A - 1) = A B = A/(1900A - 1) , #2 1/A + 1/C = 2300 A+C = 2300AC ... C = A/(2300A - 1) , #3 SUB #2 and #3 into #1 1/A + 1/(A/(1900A - 1)) + 1/A/(2300A - 1)) = 3400 1/A + (1900A - 1...
February 20, 2014

Algebra
just plug in k where you see an x
February 20, 2014

Algebra
done here http://www.jiskha.com/display.cgi?id=1392928082
February 20, 2014

Algebra
large frames ---- x small frames ---- 20-x 16x + 7(20 - x) = 176 solve, should be very straightforward
February 20, 2014

math
Pop(t) = 865 (1.15)^t , where t is the number of years
February 20, 2014

Pre algebra
There is no "answer" to y = 5x + 5 Your equation is represented by the graph of a straight line. The y-intercept is 5 , or the point (0,5) The x-intercept is -1 or the point (-1,0) Join these two points with a straight line and extend them in both directions. see: ...
February 20, 2014

Math
umhhh, Kimberly's age : Halley's age = 3 : 1 or 3/1
February 20, 2014

MATH 12
ahhh, just tried it again without the "solve" http://www.wolframalpha.com/input/?i=8500%281%2B12x%29%5E34+%2B+200%28+%281%2Bx%29%5E408+-+1%29%2Fx+%3D+193215.33 and got x = .0031041 or i = .0031041 12i = .0372492 So the equivalent annual rate of return for his ...
February 20, 2014

MATH 12
So I will assume a total time of 34 years or 408 months amount 30 years from now = 8500(1.0545)^34 + 200( 1.0025^408 - 1)/.0025 = 51641.968 + 141573.33655 = $ 193215.33 b) is quite complicated. Let the monthly return be i then 8500(1+12i)^34 + 200( (1+i)^408 - 1)/i = 193215.33...
February 20, 2014

math
a) amount = 8000 e^(12(.02)) = 8500 e^.24 = $ 10805.62 repeat procedure for the others
February 20, 2014

math
a) amount = 3500 e^(3(.0625)) = ..... same for the others.
February 20, 2014

Math
I suspect you mean: n(t)=5600/(0.5+27.5e^-0.044t) confirm my assumption before I proceed.
February 20, 2014

College Algebra
PV = 100000( 1 + .08/12)^-60 = 100000( 1.0066666..)^-60 = ...
February 20, 2014

math
2300 ----> 4600 after 1 decade so, once more gives you ??? I think your question is the incomplete version of this one, which was answered by Steve http://www.jiskha.com/display.cgi?id=1358452964
February 20, 2014

Finance
Assume an investment of $1.00 First Simple Bank: amount after 6 years = 1 + PRT = 1 + 1(.06)(10) = 1.60 Complex Bank: 1(1+i)^10 = 1.6 take 10th root of both sides ( (1+i)^10)((1/10) = 1.6^(1/10) 1+i = 1.048122.. i = .048122.. or appr 4.81%
February 19, 2014

Finance
32000 = 620 + 620( 1 - (1+i)^-59)/i My favourite webpage, Wolfram, says http://www.wolframalpha.com/input/?i=32000+%3D+620+%2B+620%28+1+-+%281%2Bx%29%5E-59%29%2Fx i = .0052576 or 12i = .06309 which is 6.309% per annum , compounded monthly (look past all that messy output to ...
February 19, 2014

Algebra
volume of 15% OJ --- x L volume of 10% OH --- 5-x L .15x + .1(5-x) = .11(5) times 100 , don't like them decimals! 15x + 10(5-x) = 55 15x + 50 - 10x = 55 5x = 5 x = 1 So 1 L of the 15% stuff and 4 L of the 10% stuff
February 19, 2014

math(algebra)
if f(x) varies directly with x, then f(x) = kx, where k is a constant given: if x=9 , f(x) = 49 so 49 = 9k k = 45/9 = 5 f(x) = 5x f(3) = 5(3) = 15 or just use a ratio 9/3 = 45/f(x) 9f(x) = 135 f(x) = 135/9 = 15
February 19, 2014

phisecs
Are you telling me you could not follow my solution to the same problem ? All you did was change one number. http://www.jiskha.com/display.cgi?id=1392776318
February 18, 2014

phisecs
What is phisecs, some small unit of time? rowing rate --- x km/h current rate --- y km/h A girl rows 11 km downstream in 2 h ---> 2(x+y) = 11 2x + 2y = 11 "Her return trip takes 4 h" ---> 4(x-y) = 11 4x - 4y = 11 first times 2 4x + 4y = 22 add to the 2nd 8x = ...
February 18, 2014

Math ~ Check Answers ~
Are you just guessing? Your second one happens to be correct, do you know why it is 2 ?
February 18, 2014

math
Poor wording of the problem. dy/dx = 8x^3 + 9x^2- 2x+ 5 y = 2x^4 + 3x^3 - x^2 + 5x + c but (2,3) lies on it 3 = 32 + 24 - 4 + 10 + c c = .... evaluate, plug c back into y = ....
February 18, 2014

math
slope of line is -1 dy/dx for y = 2/x+ k is -2/x^2 so -2/x^2 = -1 x^2= 2 x= ±2 if x = 2, 2+y = 1 ---> y = -1 so one point of contact is (2,-1) it must lie on y = 2/x + k -1 = 2/2 + k k = -2 you try the case where x = -2
February 18, 2014

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