Tuesday

April 21, 2015

April 21, 2015

Total # Posts: 29,638

**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*

**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*

**GRANTHAM**

PV = 2000 (1 - 1.06^-14)/.06 = ....
*December 30, 2014*

**Algebra 1**

I agree with Steve, I got x = 6/17 , y = 9/17 , which does not match any of the answers given
*December 30, 2014*

**algebra 2**

divide each term by -3 x^4 - 9x^2 - 400 = 0 (x^2 - 25)(x^2 + 16) = 0 x^2 = 25 OR x^2 = -16 x = ± 5 or x = ± 4i
*December 29, 2014*

**Algebra 2**

The correct statement is Salary = 2000x + 45500 , 0 ≤ x ≤ 10 , x ∈ I so it looks like B is the closest match. James's answer is incorrect, e.g. if x = 1 , the salary based on his formula is 45700 whereas it should be 47500, which is obtained with B
*December 29, 2014*

**Algebra 1**

Lucina's conclusion is correct, but based on an incorrect result. The slope of the first line is -2/3 the slope of the 2nd line is 2/3 so they are neither parallel nor parallel Lucina stated that their slopes were equal, if they had been equal, then the lines would have ...
*December 29, 2014*

**Algebra 1**

We can see that the slope of the given line is -1/4 So the slope of our new line must be 4 thus: y-5 = 4(x+3) Massage this equation to whatever form you need
*December 29, 2014*

**Precalculus**

No you have to expand (800+x)tan33 to get at the x inside the bracket. so ... 800tan33 + xtan33 = xtan35 now get all the x terms to one side 800tan33 = xtan35 - xtan33 x is a common factor: 800tan33 = x(tan35-tan33) divide both sides by tan35-tan33 800tan33/(tan35-tan33) = x ...
*December 29, 2014*

**geometry**

Let a point on the locus be P (x,y) then √(x^2 + y^2) = √((x+2)^2 + (y-5)^2) square both sides: x^2 + y^2 = (x+2)^2 + (y-5)^2 x^2 + y^2 = x^2 + 4x + 4 + y^2 - 10y + 25 4x - 10y = -29 which is the perpendicular bisector of the line joining (0,0) and (-2,5) , as ...
*December 29, 2014*

**CAL-Critical points**

F ' (x) = (x^2(1/x) - lnx(2x) )/x^4 = (x - 2x lnx)/x^4 = 0 for critical values x - 2x lnx = 0 x(1 - 2lnx) = 0 x = 0 , but for lnx to be defined, x > 0 or 1-2lnx = 0 lnx = 1/2 , x = √e x = appr 1.65 y = (1/2) / (1.65)^2 = appr .18 the critical point is appr (1.65...
*December 29, 2014*

**Algebra**

You probably mean, "completing the square", where we take the square root near the end of the process x^2 - 10x + 22 = -2 x^2 - 10x + ..... = -24 + ..... x^2 - 10x + 25 = -24 + 25 (x-5)^2 = 1 take √ of both sides x - 5 = ± √1 = ± 1 x = 5 &...
*December 29, 2014*

**mathematics**

height/15 = tan 30° take over ....
*December 29, 2014*

**Mathematics**

look for common factors first, looking at the 5x^4 and 20x^3 , that would be 5x^3 looking at the (x-7)^(-1/2) and (x-7)^(1/2) , that would be (x-7)^(-1/2) , (take the lower exponent one) also I would take out the fraction of 1/2 = (1/2)(5x^3)(x-7)^(-1/2) [x + (2/1)(4)(x-7...
*December 29, 2014*

**Mathematics**

Use the product rule for the first and the quotient rule for the second. 1. y = (5x^4)(x - 7)^(1/2) dy/dx = (5x^4)(1/2)(x-7)^(-1/2) + 20x^4 (x-7)^(1/2) I found most students find the difficulty not in finding that first derivative line, but rather in simplifying it I don't...
*December 29, 2014*

**Mathematics**

y = |x-3| ----> y = x-3 for x>3 or y = -x + 3 for x<3 for y = x-3, dy/dx = 1 , for x > 3 for y = -x+3, dy/dx = -1 , for x < 3 look at the graph of y = |x-3| http://www.wolframalpha.com/input/?i=plot+y+%3D+%7Cx-3%7C when x = 3, y = 0 for both parts of the ...
*December 29, 2014*

**maths**

contradiction ! If your tank is half full and it contains 15 L, then the full capacity must be 30 L If the tank only can hold 18 L as you said, then at 15 L it is not "half filled" If you are asking what fraction 15 is of 18 ??? 15/18 = 5/6
*December 29, 2014*

**Math**

No, the point 4,4) ----> (4,-4) after a reflection in the x-a xis but the point (4,4) ---> (-4,4) after a rotation of 90° For a point P(x,y) the slope of PO , where O is the origin is (y-0)/(x-0) = y/x For a point P1(-y,x) , the slope P1O = x/-y, which is the ...
*December 28, 2014*

**AP Calc**

f ' (x) = x(1/x) + lnx + (1-x)(-1/(1-x)) + -1(ln(1-x) = 1 + lnx -1 - ln(1-x) = lnx - ln(1-x) = ln(x/(1-x)) = 0 for a min then e^0 = x/(1-x) 1 = x/(1-x) 1-x = x x = 1/2 Proof: confirmed by Wolfram http://www.wolframalpha.com/input/?i=plot+y+%3D+x+ln+x%2B%281-x%29ln%281-x%29
*December 20, 2014*

**AP Calc**

I believe this is the same question, and answered by Steve http://www.jiskha.com/display.cgi?id=1419047350
*December 20, 2014*

**Math - Two-Step Inequalities - Please Help**

–3 > –3t + 6 3t > 6+3 3t > 9 t > 3 So for the given numbers, I see that only 4 > 3 so , yes, C is the correct answer.
*December 19, 2014*

**Math**

You have to look for some pattern Did you notice that for every 1 unit increase in the x's there is a 5 unit increase in the y's so you know it starts with y = 5x + b, we still don't know the b plug in one of the points , how about (1,2) 2 = 5(1) + b b = -3 ...
*December 19, 2014*

**math**

"Using 22/7 for pi is just not rational! " good one, they were selling t-shirts with that slogan to the math-nerds at our University of Waterloo a few years back.
*December 19, 2014*

**math**

I think 22/7 is the approximation we used for π in the "olden days" so a + b = π/2 or a and b are complementary angles Construct a right angled triangles with angles a and b along with the right angle since sina = 1/3, the missing side is √8 by ...
*December 19, 2014*

**Algebra**

x • b • y • a = (xy)(ab) = (1/37)(37) = 1
*December 18, 2014*

**math**

Elimination is a poor choice for this question. I would definitely use substitution. sub the 1st into the 2nd 2(5y) - 3y = 7 10y-3y=7 7y=7 y = 1 , then x = 5 compare this with elimination: 5y = x x - 5y = 0 multiply by 2, 2x - 10y = 0 2x - 3y = 7 subtract them -7y = -7 y = 1 ...
*December 18, 2014*

**Algebra math**

In English please.
*December 18, 2014*

**math**

number of people ---- n Company A: CostA = 25n + 50 Company B: CostB = 20n + 130 So for n = 100 CostA = 2500+50 = 2550 CostB = 2000+130 = 2130 When is CostA = CostB ? 25n + 50 = 20n + 130 5n = 80 n = 16 break-even number is 16 people.
*December 18, 2014*

**Math**

Why not just reverse the process and subtract 2 from top and bottom to get 2/3 ?
*December 18, 2014*

**Calculus**

done, look back please
*December 18, 2014*

**math**

first one is correct #2, 6.3% of $77 = .063(77) = $4.85 77+4.85 = 81.85 , so #4
*December 18, 2014*

**Calculus**

First of all you must understand what the intersection is When you intersect two planes you get a straight line, unless the two planes are parallel In this case they are not, since 1:1:-1 ≠ 2:4:-3 multiply the first by 3 3x+3x-3z = -36 subtract 2x+ 4y - 3z = -8...
*December 18, 2014*

**Math**

The inclusive vs exclusive restrictions in rational expressions always leads to debate. I restricted x = -1 and x = -2 since subbing in these values in the original yields 0/0 but subbing those values in my answer (and yours) yields a real number Since I was using the equal ...
*December 18, 2014*

**Math**

I read that as: (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) = x(x-1)/(x+3) or (x^2 - x)/(x+3) , x ≠ -1,2
*December 18, 2014*

**math**

Please number your question, how are we to know who is who and what you want done 1. assuming you want to solve 2/3n = 8 multiply each term by 3 2n = 24 n = 12 2. sub the 2nd into the 1st 4x + 3y = 13 4x + 3(-x+4) = 13 4x - 3x + 12 = 13 x = 1 back into the 2nd, y = -1+4 = 3 x=...
*December 18, 2014*

**Algebra**

good job
*December 18, 2014*

**Algebra**

first get rid of nasty fractions by multiplying each term by 3 , LCD 3x^2 - 5x + 2 = 0 which factors quite nicely. Let me know what you got
*December 18, 2014*

**algebra**

speed of boat --- x speed of current -- y x+y = 21 x-y = 5 add the two equations, and continue
*December 18, 2014*

**Algebra**

You typed the equation incorrectly, it should say y = 5 (1/2)^(t/20) so ... 4 = 5(1/2)^(t/20) .8 = (.5)^(t/20) take log of both sides log.8 = log(.5^(t/20)) log.8 = (t/20)log.5 log.8/log.5 = t/20 t = 20(log.8)/log.5) I leave the button-pushing up to you
*December 18, 2014*

**stats**

a) prob = (25/32)(24/31) = .. b) prob = (25/32)(7/31) = ... c) prob (both red) = answer to a) prob(both black) = (7/32)(6/31) = .. prob(different colour) = 1 - a) - both black
*December 18, 2014*

**math algebra**

Let the length along the front be x let the width be y let the height be z x^2+ z^2 = 25^2 = 625 , #1 y^2 + z^2 = 20^2 = 400 , #2 subtract them x^2 - y^2 = 225 , #3 also x^2 + y^2 + z^2 = 28^2 = 784 , #4 add it to #3 2x^2 + z^2 = 1009, but x^2 + z^2 = 625 from #1 so 2x^2 + z^2...
*December 18, 2014*