Wednesday
May 27, 2015

Posts by Reiny


Total # Posts: 30,077

math
so you need 15(10) or 150 man-days to do the job so with 6 men you would need 150/6 or 25 days or use a ratio 15/6 = x/10 6x = 150 x = 25
January 9, 2015

Math
1 e^(3r) = 2 take ln of both sides 3r lne = ln2 , but lne = 1 3r = ln2 r = ln2/3 = .231.. So you will need a continuous rate of growth of 23.1 % good luck on that one.
January 9, 2015

Math
g(x)=(2x^2-7x+3)/(x-3) = (x-3)(2x-1)/(x-3) = 2x-1 , x ≠ 3 ≠ f(x)
January 9, 2015

Marh
just translate your English sentence into "Math" 5 + 8x = 60 + 3x easy to solve
January 9, 2015

Math
if f(x) = g(x), it must be true for all values of x (all we need is ONE exception and they would not be equal) f(1) = 6 + -11/5 = a fraction g(1) = 3-4 = -1 so f(x) is NOT the simplified form of g(x)
January 9, 2015

Math
(-9,-90°) this would point you clockwise 90° or 270° using the standard rotation. You would then go in the opposite direction for 9 units so equivalent to (9, 90°) (9,270°) would be the same as (9, -90°)
January 9, 2015

Math
I will put in the brackets for you, (you obviously ignored my comment about brackets from yesterday) (x^2-2x)/(x+1) * (x^2-1)/(x^2+x-6) = x(x-2)/(x+1) * (x-1)(x+1)/((x+3)(x-2)) you take over I see nice cancellations
January 9, 2015

Math
x/( (x-4)(x+1)) - 4/(x+1) LCD is (x-4)(x+1) = ( x - 4(x-4) )/((x-4)(x+1)) = (x - 4x + 16)/(x^2 - 3x - 4) = (16 - 3x)/(x^2 - 3x - 4) , x ≠ -1,4 btw, I recall Damon answering this same question for you yesterday
January 9, 2015

Math
7(cos 5pi/6 +isin 5pi/6) / -2(cos pi/2 +isin pi/2) = 7(-√3/2 + i/2) / (-2(0 + i)) = (7/2)( -√3 + i) / (-2i) * i/i = (7/2)(-√3i + i^2)/(-2i^2) = (7/2)(-1 - √3 i)/2 = (-7/4)(1 + √3 i) your 7 square root 3/4 i part is ambiguous, it needs brackets to ...
January 9, 2015

Math
Two concerns about your post: 1. For the first equation, did you mean 4x + 2y = 6 ? 2. This is clearly an assignment which will be marked, since you are showing how many points each answer is worth. We do not do a student's assignment for them. Show your steps and the area...
January 9, 2015

Math
I got -10i Did you get your answer by expanding -10((cos pi/3 +isin pi/3)(cos pi/6+ isin pi/6) ? my 2nd-last line was: -10( cos π/2 + i sin π/2)
January 9, 2015

Math
Steve answered this question for you yesterday. Always check back before re-posting the same problem.
January 9, 2015

geometry honors
To be a ||gm , opposite sides must be equal 7y-8 = 5y and 6x-3 = 3x+12 7y - 8 = 5y 2y = 8 y = 4 6x-3 = 3x+12 3x = 15 x = 5 Since the given information about x and y match those solutions, yes, it is a parallogram or just sub in the given values into the 4 different expressions...
January 8, 2015

Math
nothing to simplify did you mean (e^27)x or e^(27x) the first one is appr 5.32 x 10^11 x the other one stays as is
January 8, 2015

Ap calc
You will need brackets y= (e^x - e^-x) / (e^x + e^-x) wonder what would happen if we multiply top and bottom by e^x = y= (e^x - e^-x) / (e^x + e^-x) * (e^x/e^x) = (e^2x - 1)/(e^2x + 1) now dy/dx = ( (e^2x + 1)(2e^2x) - (e^2x - 1)(2e^2x) )/(e^2x + 1)^2 = (2e^4x + 2e^2x - 2e^2x...
January 8, 2015

math
wouldn't there now be 6 white balls left out of the remaining 19 ? so ....
January 8, 2015

math
make sure you type or enter (-5)^6 your expression of -5^6 = - 15625 according to the order of operations.
January 8, 2015

Math
The point (5,-2) lies in the 4th quadrant. So plot it and complete the right-angled triangle (draw a vertical to the x-axis) so x = 5, y = -2 , r = √(25 + 4) = √29 we know sinØ = -2/√29 then cscØ = -√29/2
January 8, 2015

Note to Alex - Math
Alex, yesterday I pointed out to you how important it is to include brackets in this format of typing your questions. http://www.jiskha.com/display.cgi?id=1420682753 You have ignored this and continue to type in this ambiguous way for your previous set of questions. Are you ...
January 8, 2015

math
sketch y = x^3 then reflect the part which is below the x-axis about the x-axis http://www.wolframalpha.com/input/?i=plot+y+%3D+%7Cx%7C%5E3
January 8, 2015

Math
h(t) = -16t^2 + 96t + 60 v(t) = -32t + 96 at max height , v = 0 -32t + 96=0 32t = 96 t = 96/32 = 3 h(3) = -16(9) + 96(3) + 60 = 204 or h(t) = -16(t^2 - 6t + 9-9) + 60 = -16( (t-3)^2 - 9) + 60 = -16(t-3)^2 + 144 + 60 = -16(t-3)^2 + 204 this has a vertex of (3,204) thus a max of...
January 8, 2015

College Algebra
So I will use two variables in the solution let the amount of 10% solution used be x cc let the amount of 5% solution be y cc "A pharmacist wants to mix two solutions to obtain 100 cc" ---> x + y = 100 the new solution must contain 8% , so .08(100) 2nd equation: ....
January 7, 2015

math
Thanks for the correction , Steve
January 7, 2015

math
let the smaller angle be x° then the larger is 7x + 10 but ... x + 7x + 10 = 180 take over
January 7, 2015

Math 10 aw
let that distance be h , (the hypotenuse) I see it as sin18° = 125/h h = 125/sin18 = ...
January 7, 2015

Math
You must know that for any linear equation written in the form y = mx + b the slope is m and the y-intercept is b so, what do you think?
January 7, 2015

sixth grade math
you are welcome
January 7, 2015

sixth grade math
There are 24 seats open in a theatre, shown as 3 rows. How many seats are there in each of the three rows. let the number of seats be y 24/y = 3 y = 8
January 7, 2015

Math
The largest quotient can be obtained when the numerator is largest and the denominator is smallest so since in x/y, x goes from 10 to 20 and y goes from .2 to 5 the largest quotient is 20/.2 which is 100 the farthest vertex would be (-x,y) , the others would be (-x,0) , (0,y) ...
January 7, 2015

Math
PV = 12000(1 + .09/12)^-72 = 12000(1.0075)^-72 = $7007.08
January 7, 2015

Math
Why not type x divided by x^2-3x-4 subtracted by 4 divided by x +1 as x/(x^2 -3x - 4) - 4/(x+1) then = x/( (x+1)(x-4) - 4/(x+1) now your common denominator is (x+1)(x-4) take over
January 7, 2015

Math
As you typed it ... 1 + 2x/x+4=3/x-1 1 + 2 + 4 = 3/x - 1 8 = 3/x 8x = 3 x = 3/8 I will assume you meant: 1 + 2x/(x+4) = 3/(x-1) multiply each term by (x+4)(x-1) (x+4)(x-1) + 2x(x-1) = 3(x+4) x^2 + 3x - 4 + 2x^2 - 2x = 3x + 12 3x^2 - 2x - 16 = 0 (3x - 8)(x + 2) = 0 x = 8/3 or x...
January 7, 2015

Math
for any function y = sin (kx) or cos (kx) the period is 2π/k so for yours the period = 2π/(1/7) = ...... I think you just guessed at 2π, because it makes no sense otherwise.
January 7, 2015

math
recall that when dividing by a fraction we multiply by its reciprocal y/4 ÷ 1/4 = (y/4)(4/1) = y
January 7, 2015

math
is there a question ?
January 7, 2015

Algebra
Easiest way to graph a straight line on a grid is to find their x and y intercepts. for this one: let x = 0 , then y = 2 let y = 0 , then x = 2/3 you now have two points (0,2) and (2/3 , 0) plot them , join them and you are done
January 6, 2015

Math
I will try to explain with an example Suppose you have the product (4x5x6) which would be 120 So if we double that we would get 2 x (4x5x6) or 240 Would we multiply the 2 by each of the factors of the original product ? Of course not. We would multiply by only one of the ...
January 6, 2015

math
reduce the ratio: 2.8 : 1.25 = 280 : 125 = 56 : 25 let the ratio of the ribbons be 56x : 25x "The difference in the length of the shorter pieces is 80.6 cm. " This makes no sense, I will assume you meant that the difference in the length of the two pieces is 80.6 56x...
January 6, 2015

algebra
use this probability calculator instead of tables Just enter the date, and click on the greater than option http://davidmlane.com/hyperstat/z_table.html you should get .0228
January 6, 2015

Math
wouldn't you you just set 25t - 80 = 60 and solve ? looks pretty straighforward
January 6, 2015

college pre-calculus
For any polynomial equation with rational coefficients, complex roots must occur as conjugate pairts, that is, if one root is 1+i, there has to be another one 1 - i so, including the root of -1, the equation could have been (x+1)(x - (1+i) )(x - (1-i) ) = 0 (x+1)(x-1-i)(x-1+i...
January 6, 2015

math
r^2 = 200^2 + 50^2 = 42500 r = √42500 = 50√17 tanØ = -50/200 = -1/4 Ø = 165.96° so using the (r,Ø) notation , her position is (50√17, 165.96°)
January 5, 2015

Math
e(x + 1) + e(x - 4) = ex + e + ex - 4e = 2ex - 3e or = e(2x-3)
January 5, 2015

Math
All kinds of missing information: - how much more each month does he deposit ? - are the increases each month the same amount? - does he not get any interest in his savings account? (if not, he might as well put each month's deposit in a sock under his bed, at least he won...
January 5, 2015

math
This looks like silly math pedagogy to me. For heaven's sake : just learn and memorize the 6 times table
January 5, 2015

Math
L#L-##LL ---> 25x10x25x10x10x25 =
January 5, 2015

Math
Not familiar with this notation and the ( or [ are confusing. In the "good ol' days" way: domain: any real number range : y ≤ 0 I will leave it up to you to identify the matching answer
January 5, 2015

Mathematics
There is really no need to have brackets on the RS but I would mentally look at it as (2x)(y^2) so the product rule is more obvious so ..... 3/(3x) + (dy/dx)/y = (2x)(2y dy/dx) + (y^2)(2) multiply each term by y y/x + dy/dx = 4xy^2 dy/dx + 2y^3 dy/dx - 4xy^2 dy/dx = 2y^3 - y/x...
January 5, 2015

Mathematics
I have now shown you how to do several of these kind of derivatives. It is time for you to show us some of your own efforts. What have you got so far ?
January 5, 2015

Mathematics
recall that the basic log derivatives apply to logs with base e then let y = log5 ((2x+1)/(3x-1)) = log5 (2x+1) - log5 (3x-1) dy/dx = (1/ln5)(2/(2x+1)) - (1/ln5)(3/(3x-1)) = (1/ln5) (2/(2x+1) - 3/(3x-1) )
January 5, 2015

Math
Did this one yesterday. make sure the points are the same http://www.jiskha.com/display.cgi?id=1420371208
January 5, 2015

Mathematics
y' = 2(sin 4x cos 3x)( sin4x(3)(-sin3x)) + cos3x(4)cos4x))
January 5, 2015

Mathematics
That was clearly a typo, good for you to catch it
January 5, 2015

Mathematics
or y = x^3/cosx y' = (cosx(3x^2) - x^3(-sinx))/cos^2x = (3x^2 cosx + x^3 sinx)/cos^2x now do it again
January 5, 2015

Mathematics
I assume you differentiating with respect to x ? 3x^2 = y(-sinx) + dy/dx(cosx) dy/dx = 3x^2 + ysinx d(dy/dx)/dx = 6x + dy/dx sinx + ycosx = 6x + (3x^2 + ysinx)sinx + ycosx = 6x^2 + 3x^2sinx + ysin^2 x + ycosx check my work, should have written it on paper first
January 5, 2015

math
multiply 1st by 3 9x - 3y = 0 4x + 3y = 26 add them: 13x = 26 x = 2 back into original #1 3(2) - y = 0 -y = -6 y = 6 x = 2, y = 6
January 5, 2015

business math
amount = 3000( 1 + .06/12)^12 = 3185.03 Didn't know tables were still being used in this topic.
January 5, 2015

math,trigonometry
I just did this one: http://www.jiskha.com/display.cgi?id=1420462410 for #2. using the sine law: sinB/7 = sin88/8 sinB = 7sin88/8 = .8744... angle B = 60.98° or angle B = 119.18° using the CAST rule case1: B = 60.98, A = 88 , then C = 180-88-60.98 = 31.02° or to ...
January 5, 2015

math, solving Oblique triangle
Notice one of the fractions is a constant, so use b/sin49 = 10/sin16 b = 10sin49/sin16 you should get appr 27.38 then c/sin115 = 10/sin16 c = 10sin115/sin16 = 32.88
January 5, 2015

algebra
So what is 9 x 8 ?
January 5, 2015

algebra
yes
January 5, 2015

math/ ratio
ban : pine : pap = 21 : 15 : 9 = 7 : 5 : 3
January 5, 2015

Mathematics
use your rules of logs to simplify this messy expression I will assume you meant: y = ln [ (2x-1)/(1+x) ]^(1/2) = (1/2)( ln(2x-1) - ln(1+x) ) dy/dx = (1/2)( 2/(2x-1) - 1/(1+x) ) = 1/(2x-1) - 1/(2(1+x))
January 5, 2015

Algebra I
number of adult tickets --- x number of student tickets -- y x + y = 64 2.5x + y = 109 subtract the two equations to get x = ... then sub back into the first equation to get y
January 4, 2015

Pre-Calc
John, I don't know how you got 63 when t=5 I got 44.48 when t = 5 We could have used a sine curve height = 30sin ((πt/8)(t-4) ) +33 check: when t = 0 , height = 3 , ok when t = 8 , height = 63, ok when t = 4, height = 4.48 , the same result we get when we use Steve&#...
January 4, 2015

Math
Cherie, You are using decimals and rounding off your answer before you are substituting. look at Quidditch's last line 2.8x = 60 x = 60/2.8 = 600/28 = 150/7 or 21 3/7 now y = 10 - 2.2(150/7) = 10 - (22/10)(150/7) = 10 - 330/7 = -260/7 or -37 1/7 since "anything"/...
January 4, 2015

maths
dy/dx = 6x^2 - x - 1 = 0 at the turning points (3x + 1)(2x - 1) = 0 x = -1/3 or x = 1/2 sub those values into original equation to get the whole points y'' = 12x-1 when x = -1/3, y'' is negative, so x = -1/3 will yield a maximum point when x = 1/2 , y''...
January 4, 2015

maths
dy/dx = 8x so at (2,21) , the slope is 16 y - 21 = 16(x-2) etc
January 4, 2015

math
a + 8d = 52 (12/2)(2a + 11d) = 414 or 2a + 11d = 69 solve these two equations for a and d
January 4, 2015

Analytical Geometry
looks like plain ol' Pythagoras base^2 + 8^2 = 10^2 bse^2 = 100-64 = 36 base = √36 = 6 slope = rise/run = height/base = 8/6 = 4/3 Make a sketch of the situation Place the 6-ft man on the base 3 ft from the base. Is he below the ladder or did his head hit the ladder? ...
January 4, 2015

math
I can't see your diagram, but the diagonal of the square from (4,1) to (5,8) is also the diameter of the circle length = √(1^2 + 7^2) = √50 = 5√2 so the radius of the circle must be 2.5√2 perimeter of circle = 2πr or dπ = √50π...
January 4, 2015

Math
mmmh, diagonals in a triangle ? Label your given points A, B, and C in the corresponding order. Clearly AB is a horizontal line, thus AB = 8 AC = √(1^2 + 9^2) = √82 BC = √(7^2 + 9^2) = √130 perimeter = 8 + √82 + √130 = appr 28.5
January 4, 2015

math
the number is 10y + x 10y + x = 9(x+y) 10y + x =9x + 9y y - 8x = 0 or y = 8x since both x and y must be ≤ 9, the only choice for x = 1 so y = 8 and the number must be 81
January 4, 2015

maths
100000 = 3000( 1 - 1.0041666...^-n)/.0041666.. .3888.. = 1 - 1.0041666..^- 1.0041666..^-n = .61111.. take log of both sides and use log rules - n = log .61111../log 1.0041666.. -n = - 118.44 n = 118.44 So there are 118 full payments of 3000 plus another partial payment at ...
January 4, 2015

Maths
done, see the two previous posts of the same question.
January 4, 2015

Maths
net price = (200)(.9)(.95)(.98)(.95) = 159.20
January 4, 2015

Maths
Always check back to see if your previous post of the same question has been answered before reposting it. http://www.jiskha.com/display.cgi?id=1420301789 This will prevent unnecessary duplication.
January 4, 2015

ALGEBRA
i = .03/12 =.0025 n = 12(20) = 240 amount = 200 ( 1.0025^240 - 1)/.0025 = .....
January 3, 2015

Math - Please help
slope of given line is 4 since the new line is parallel, its slope must also be 4 let y = 4x + b using the point (1,-3) -3 = 4(1) + b -7 = b new equation in slope-intercept form is y = 4x - 7
January 3, 2015

Maths
You need one more piece of information. The way it stands ar^2 = 7 r^2 = 7/a r = ±√(7/a)
January 3, 2015

ALGEBRA
You have to know the formulas for the general term and the sum of n terms of an arithmetic sequence term6 = a + 5d = 48 sum6 = (6/2)(2a + 5d) = 300 3(2a + 5d) = 300 2a + 5d = 100 subtract the two two equations: a = 52 back in a+5d = 48 52+5d = 48 5d = -4 d = -4/5 so the first ...
January 3, 2015

math
yup, there are lots of them let Google be your friend
January 3, 2015

trig
In other words.... we have to prove that 2sinxcosx + 4cos^2 x - 1 = tan^2 x - 2tanx - 3 I had my doubts about this "identity" so I tried any arbitrary value of x (remember , all we need is ONE exception and the identity is not true) I tried x = 21° LS = 2sin21 ...
January 3, 2015

calculus
use the product rule .. dy/dx = x^3 (5/5) + 3x^2 ln(5x) = x^2 + 3x^2 ln(5x) or = x^2(1 + 3ln(5x) )
January 3, 2015

^NeEd HeLp^
What language are you using? The majority of questions posted here are in English.
January 3, 2015

Algebra 1
Since both equations were in the form y = ... he simply replaced the y value of the first equation with the y value of the second. Some texts call this the "comparison" method e.g. if a = b and c = b , then a = c yes, you could use elimination after some doctoring of...
January 3, 2015

trigonometry
I see a right-angled triangle with hypotenuse of 60 and a base angle of 52° sin52 = y/60 --> y = 60sin52 = ... cos52 = x/60 ---> x = 60cos52 = ...
January 3, 2015

AP CaLC. AB
if v(t) = t^2 - 3cos(t) then s(t) = (1/3)t^3 - 3sin(t) + c given : when t = 0 , s(0) = 0 0 = 0 - 3sin0 + c c = 0 so when v = 0 0 = t^2 - 3cos(t) using Wolfram, I got t = 1.13062 where does x enter the picture, your function was defined in terms of t http://www.wolframalpha.com...
January 3, 2015

retype - calculus
Let me type this again in proper English. (Can I blame it on my keyboard ? ) Clearly the vertex of this parabola is (-2,-4) and it opens downwards. Thus it cannot possible reach the x-axis, thus there are no x-intercepts for the y-intercept, in you let let x = 0 and evaluate ...
January 3, 2015

calculus
clearly the vertex of this parabola is (-2,-4) and it opens downwards. This is cannot possible reach the x-axis, thus no x-intercepts for the y-intercepts, in you head let x = 0 and evaluated to get y = -4-4 = -8
January 3, 2015

Calculus
h ' (x) = 3x^2 + b = 0 at a critical point if (2,-4) is a critical point, 3(4) + b = 0 b = -12 but (2,-4) also satisfies h(x) -4 = 8 - 12(2) + c c = 12 thus h(x) = x^3 - 12x + 12
January 2, 2015

Statistic
for test1 prob correct = 1/4 prob wrong = 3/4 i) could be c or wc or wcc , (c for correct, w for wrong) prof (of that) = 1/4 + (3/4)(1/4) + (3/4)^2 (1/4 = 37/64 ii) less than 4 correct ---> none correct + 1 correct + 2 correct + 3 correct = C(8,0) (1/4)^0 (3/4)^8 + C(8,1)(1...
January 2, 2015

Physics 1
v = -9.8 t so when t = 10 s v = -9.8(10) = -98 m/s The negative indicates the direction of the stone.
January 1, 2015

algebra 2
I will assume you meant to type (x^2 + 8x + 15)/(x+5) and you want to simplify it = (x+5)(x+3)/(x+5) = x+3 , x ≠ -5
January 1, 2015

math
The number of subsets of 6 from 18 is C(18,6) = 18!/(6!12!) = 18564
January 1, 2015

regneing
Very strange question. 2 x 8084506040 ≠ 8002408082
December 31, 2014

Math
You would use ADDITION No need for multiplication, division, or fractions in this case. 360+240=600
December 31, 2014

MATH
If you have two points (a,b) and (c,d) then the distance between them is √( (a-c)^2 + (b-d)^2 ) (notice that since we are squaring the difference, it really would not matter in which direction you are subtracting) e.g. for R(-2,1) and S(-5,1) RS = √( (-2+5)^2 + (1-...
December 31, 2014

Algebra
Olivia, why did you not evaluate the equation given to you in the first reply ? it gives a time of 2.777... or 2.8 years Bob gave you the calculation using compound interest, the most likely scenario in our 21st Century, and the time for this real-life case would be 2.65 years...
December 31, 2014

Algebra 1
What is this? Are you expanding 2x(3xy + 4y² + 8y) ? Then it would simply be = 6x^2 y + 8x y^2 + 16xy What you did is pure mathematical gibberish
December 30, 2014

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