Saturday

April 30, 2016
Total # Posts: 40,015

**Stats**

you can play around with Z table stuff at http://davidmlane.com/hyperstat/z_table.html
*April 17, 2016*

**mathematics-need help urgently please**

v = x^2h, so h = 1000/x^2 a = 2x^2 + 4xh = 2x^2 + 4000/x da/dx = 4x - 4000/x^2 = 4(x^3-1000)/x^2 so, da/dx = 0 when x=10 a = 2*100 + 4*10*1000/100 = 600 as usual, area is minimum when the shape is a cube.
*April 17, 2016*

**PRECALC**

you know that anything more complicated than a quadratic is tough, so look for low-hanging roots: ±1,±2,±3. A little synthetic division yields P(x) = (x-3)(x+1)(x^2+1) now it's easy.
*April 17, 2016*

**precalc**

of course -b/2a does not work. It's not a quadratic. Furthermore, x = -b/2a gives the location of the vertex of a quadratic, not the roots. You know that any rational roots must be among ±1,±2,±5,±10 A little synthetic division shows that p(x...
*April 17, 2016*

**precalc**

d: the arccos has principal vales from 0 to π. cos(-4π/3) = -1/2 cos^-1(-1/2) = 2π/3 f: cos(13π/12) = -cos(π/12) = -x arccos(-x) = π-arccos(x) = 11π/12 The others look good. Be careful with the principal values stuff.
*April 17, 2016*

**dividing fraction with brackets**

5/6 - 2(-1 3/4)/(5 1/5) 5/6 - 2(-7/4)/(26/5) 5/6 - 2(-7/4)(5/26) 5/6 + 35/52 (5*32 + 35*6)/312 470/312 235/156
*April 17, 2016*

**Math**

r:b = 3:2 = 9:6 b:g = 3:7 = 6:14 r:b:g = 9:6:14 assuming none of the ones removed were red, 1/4 (9x+6x+14x - 7) = 9x Hmmm. I get x = -1 better double-check my math and the problem.
*April 17, 2016*

**maths**

by definition, x = arccos(3/5) of course, x might be in quadrants I or IV. cos(.9273) = 0.6 cos(5.3559) = 0.6 x = 2kπ ± 0.9273
*April 17, 2016*

**Trigonometry**

Draw your triangle in standard position. Then you have r=5 secθ = r/x = 5/-3
*April 17, 2016*

**maths**

The first digit must be 1,2 or 3 That leaves 4 digits to shuffle for the others. So, the total number is 3 * 4! = 72
*April 17, 2016*

**calculus help**

or, you can expand cos^10(x) as combinations of single powers of cosines: 512 cos^10(x) = 126 + 210cos(2x) + 120cos(4x) + 45cos(6x) + 10cos(8x) + cos(10x) those terms are easy to integrate. They come from repeated use of cos(2x) = 2 cos^2(x)-1 cos(4x) = 2cos^2(2x)-1 and so on.
*April 17, 2016*

**calculus help**

This has to be done in several steps using integration by parts. To see how it works, take a look at https://en.wikipedia.org/wiki/Integration_by_reduction_formulae
*April 17, 2016*

**Calcus**

oh. right. you want to use calculus. f' = 2x+k f'=0 at x = -k/2 f(-k/2) = k^2/4 + k(-k/2) + 2 = k^2/4 - k^2/2 + 2 = -k^2/4 + 2 we want the minimum to be 1, so -k^2/4 + 2 = 1 k^2/4 = 1 k^2 = 4 k = ±2 as above
*April 17, 2016*

**Calcus**

try completing the square. x^2+kx+2 = x^2 + kx + (k/2)^2 + 2 -(k/2)^2 = (x + k/2) + 2 - k^2/4 Now you have the vertex form of the parabola, with the vertex at x = -k/2. At that point, the minimum is 2 - k^2/4 So, now just set 2 - k^2/4 = 1 k^2/4 = 1 k^2 = 4 k = ±2 f(x...
*April 17, 2016*

**HUNGER GAMES**

google is your friend
*April 17, 2016*

**algebra**

oops. |2n+1| = (2n+1) or -(2n+1) if -(2n+1) = 19 -2n = 20 n = -10 check: |(3(-10)+1-(-10)| = |-30+1+10| = |-19| = 19
*April 17, 2016*

**math**

I think it's supposed to read "1/3 of them are blue." 1/3 of 21 = 7
*April 17, 2016*

**Calculus**

as usual, the volumes can be done using shells (v = 2πrh) or discs (washers) (v=πr^2), both multiplied by the thickness (dx or dy). I'll show both integrals (i) v = ∫[0,ln3] π(e^(2x))^2 dx = 20π v = π(1^2)(ln3) + ∫[1,9] 2πy(ln3 - 1...
*April 17, 2016*

**math**

that's alpha and beta. I'll use x and y for ease of typing. since the angles are complementary, cos(x) = sin(y) cos(x)*cos(y) = sin(y)*cos(y) = 1/2 sin(2y) since sin has maximum value of 1, ...
*April 17, 2016*

**MATHS**

times D w by D h by D l
*April 17, 2016*

**math**

1 - 3/7 = 4/7
*April 17, 2016*

**Math**

3(-1) / ((-1)^2-(-1)-12) = -3/-10 = 3/10 = 0.3 you are correct
*April 16, 2016*

**algebra**

since time = distance/speed, if his original speed was x, 90/x + 90/(2x) = 3 x = 45
*April 16, 2016*

**math**

if the original cost is c, and her selling price is p, then .90p = .81c * 1.20 p = 1.08c or, 8% more than the original price
*April 16, 2016*

**Math**

as with all circles, C = 2πr
*April 16, 2016*

**Math**

ATT: c(m) = 12.00 for m <= 250 12.00 + .05(m-250) for m>250 T Mobile: c(m) = 3.00 for m <= 30 3.00 + .10(m-30) for m > 30 Virgin: c(m) = 20.00 for m <= 400 20.00 + .10(m-400) for m>400 Now just figure the cost for various amounts of minutes, especially where ...
*April 16, 2016*

**math**

did that two hours ago: http://www.jiskha.com/display.cgi?id=1460822853
*April 16, 2016*

**Math**

u = 4n 19n+9u = 7500
*April 16, 2016*

**math**

(7 -3)(x) = (21) (5 -1)(y) (85) formatting not good here.
*April 16, 2016*

**math**

x+y = 600 1.22x + 1.08y = 600
*April 16, 2016*

**Algebra**

well, f(x) = (5x-1)(x+1) when is that zero?
*April 16, 2016*

**maths help polynomial agn**

how does all that stuff on the left relate to 1.004? In any case, just use your calculator. or, type it in at google. (2+√3)^6+(2-√3)^6 = 2702
*April 16, 2016*

**Maths help - not polynomial**

this is not a polynomial. It is just an expression. 4^5 - √5^5 = 4^5 - 25√5 not much to do with that. I suspect a typo
*April 16, 2016*

**Math**

(1/2)(3x)(x+7) = 66 now just expand and solve for x. Then the height is x+7.
*April 16, 2016*

**Math**

y = 1/x zx = 12/35 zy = 15/7 zx = 12/35 z/x = 15/7 12/(35x) = 15x/7 84 = 525x^2 x^2 = 84/525 = 4/25 x = 2/5 y = 5/2 z = 6/7
*April 16, 2016*

**Math (Geometry)**

the exterior angles always sum to 360.
*April 16, 2016*

**Calculus (Im I Doing This Right???? Im Unsure)**

either way works fine. Plug in the point before or after. The first way gets you to 4x-6, and then you can use that to find the slope at any point, without having to go through all of the steps each time.
*April 16, 2016*

**Alegebra**

the area increases as the square of the linear scale factor. So, it would increase by a factor of 1.10^2
*April 16, 2016*

**Further math**

n/2 (2*4 + (n-1)*3) = 209 1/2 (3n^2+5n) = 209 3n^2+5n-418 = 0 (3n+38)(n-11) = 0 n=11
*April 16, 2016*

**maths help me!!!**

you have several values, each of which has two cases. |x+1| = x+1 if (x+1) >= 0 |x+1| = -(x+1) if (x+1) < 0 So, you need to set up the inequalities and check both values for each || quantity. As a help, see the graphs at http://www.wolframalpha.com/input/?i=|x%2B1|-|x|%...
*April 16, 2016*

**Math**

20ml = 0.02L, so 37800L / (.02L/s) = 1,890,000 seconds = 21 days 21 hrs
*April 16, 2016*

**Math**

x * 1.10 * 1.15 = 10120
*April 16, 2016*

**Algebra 2**

describe the diagram. Whatever the layout, I'm sure the maximum area will be when the fence is divided equally among lengths and widths.
*April 16, 2016*

**maths (jnv arihant) work and time**

in 20 days, only 60/132 = 15/33 of the wall is done. So, that means each man has done 15/528 of the job. So, 18/33 remains. At this point, I get confused. What does working 6 as many hrs mean? Surely they cannot be working 6 times as many hours. Anyway, see what you can do ...
*April 16, 2016*

**Algebra 2**

well, just solve -16t^2 + 40t + 6 = 10 You'll get two answers, one going up and one coming back down.
*April 16, 2016*

**math**

(3n+4)/(n+2) = 3 - 2/(n+2) So, if n=0, that's 3 - 2/2 = 2 n = -1, it's 3 - 2/(-1) = 4 If n is any other value, the fraction is not an integer.
*April 16, 2016*

**maths**

if BC and CA are lines, then the locus of points equidistant from both lines is the bisector of the angle between them.
*April 16, 2016*

**maths**

not sure what "partly" means, but if direct, then y = k√x, so k=1, and y=√x If inverse, then y=k/√x so k=1, y=1/√x
*April 16, 2016*

**maths**

The distance from (1,2) to the line 3x-4y-2=0 is |3*1-4*2-2|/√(3^2+4^2) = 7/5 If the parabola is expressed in the form y^2 = 4ax, then the distance from the directrix to the vertex is a. So, 4a = 28/5
*April 16, 2016*

**math**

a = 3w^2 + 2(wh + 3wh) = 3w^2+8wh since a=3600, h = (3600-3w^2)/8w The volume is 3w^2h = 3w/8 (3600-3w^2) find the derivative, set it to zero, and you will find that w=20. So, h=15 and the maximum volume is 20x60x15 = 18000
*April 16, 2016*

**Math**

75 - x/2 - 6 = 32
*April 15, 2016*

**Calculus (Im I Doing This Right???? Im Unsure)**

you are right on.
*April 15, 2016*

**Geometry**

it has moved left 5 and up 4
*April 15, 2016*

**algebra**

so, just plug in 6 for t.
*April 15, 2016*

**math**

x^2+5x-6 < 0 (x+6)(x-1) < 0 you know that the parabola opens upward, and that it crosses the x-axis at x = -6 and x=1. So x^2+5x-6 < 0 in the interval (-6,1) or, brute-forcing it, if x>1, both factors are positive if x < -6, both factors are negative. in (-6,1) ...
*April 15, 2016*

**Math**

45% of 40 is 18 after x girls join, (18+x)/(40+x) = 56/100 Now just find x
*April 15, 2016*

**Algebra**

differences: 1 3 5 7 2 2 2 so, the function is a quadratic
*April 15, 2016*

**math.**

x is 3 if x < 3 x is 4 is x >= 3 Given so few points, it is possible to posit any number of rules.
*April 15, 2016*

**Math**

2(w + 5w-8) = 140 find w, then the length. Volume is l*w*d
*April 15, 2016*

**math**

Just list them: 3+3+3+3+3 3+3+3+3+2+1 ... 1+1+1+1+1+1+1+1+1+1+1+1+1+1+1
*April 15, 2016*

**algebra**

you have the intercepts. Plot those two points and draw a line through them. That is the graph.
*April 15, 2016*

**pc parabola**

I'd have stopped a step earlier: y = (x+4)^2/38 - 121/38
*April 15, 2016*

**Math**

I'd say yes, except for that pesky minus sign. I suspect a typo. D is correct if the original expressions is -x(5x-4)
*April 15, 2016*

**Math**

some kind of logistic function
*April 15, 2016*

**maths**

m = s+4 m+8 + s+8 = 3(m+s) or, m-s = 4 m+s = 8 m = 6
*April 15, 2016*

**mats**

5(a+4d) = 6(a+5d) a = -10d T11 = a+10d = 0 check: a=10, d=-1 10,9,8,7,6,5 5*6 = 6*5 a=-5, d=1/2 -5,-4.5,-4,-3.5,-3,-2.5 5(-3) = 6(-2.5) = -15 In both cases, T11 = 0
*April 15, 2016*

**Percent**

If the true value was 50, then Julian got 52.5 Amanda got 47.5 Clearly the actual and percent errors were the same in both cases. Julian's error was +5%, Amanda's was -5%
*April 15, 2016*

**maths**

e^x = x since e^x is always positive, there are no negative roots. Since the slope of y=x is 1, and the slope of y=e^x is greater than 1 for positive x, then since e^0>0, the two graphs never intersect. In short, there are no real solutions.
*April 15, 2016*

**Science**

would that be Capt. Jack Sparrow?
*April 15, 2016*

**math**

You have a scaled-up 3-4-5 right triangle.
*April 15, 2016*

**Percent error math**

surely the change would be 5 * -3/2 = -15/2
*April 15, 2016*

**maths**

The question as stated has no solution. clearly the boys' %age is 80% of the girls'
*April 15, 2016*

**Math**

well, sin(2t) varies from -1 to 1.
*April 15, 2016*

**Math Trig**

correct. How can you be stuck there? Surely by the time you have learned trigonometry, you know how to work with fractions ... ? hint: 1 = 169/169
*April 14, 2016*

**Algebra**

j = 3g g = b/2 s = 2(j+b) s = 60 solving those, we get Greg is 6. So, Jane is 8.
*April 14, 2016*

**Math**

she rose 3*25 = 75 ft clearly she started up from -195-75 = -270 ft
*April 14, 2016*

**Math**

24:18 = 4:3
*April 14, 2016*

**physics**

surely you remember the first formula ever taught in physics: F = ma just plug in your numbers.
*April 14, 2016*

**Math**

Looks like 0.4 * 0.75
*April 14, 2016*

**Precalculs**

4x^2/36 + 49y^2/36 = 1 x^2/9 + y^2/(36/49) = 1 a = 3 b = 6/7 c^2 = a^2-b^2 = 9-36/49 = 405/49 c = 9√5/7 You found the vertices ok. They are at (±a,0) The foci are at (±c,0)
*April 14, 2016*

**math**

google is your friend. You can start here: http://mathforum.org/library/drmath/view/51708.html
*April 14, 2016*

**Algebra**

8n^2 - 6n + 7n^2 - 4n +5 8n^2+7n^2 -6n-4n + 5 15n^2 - 10n + 5 do the 2nd one the same way. Collect all the terms with the same powers, then add up the coefficients.
*April 14, 2016*

**Polynomials**

(m^2 – m + 3) + (m – 1) m^2-m+3+m-1 m^2-m+m+3-1 m^2+2 (4x^2 – 2x – 1) – (–3x^3 + 2) 4x^2-2x-1+3x^3-2 3x^3+4x^2-2x-1-2 3x^3+4x^2-2x-3
*April 14, 2016*

**Help please**

they are the numbers multiplying the variables. so, -4 is just a constant, not a coefficient. 5,2 are the coefficients.
*April 14, 2016*

**Math - Please check!**

they all look good to me.
*April 14, 2016*

**Maths-equation**

Try letting a = x+y b = y+z c = x+z Then you have a+b = 5ab b+c = 7bc a+c = 6ac Now see what you can do with that.
*April 14, 2016*

**Math**

The 1st alloy (x) is 2/5 iron and the 2nd alloy (30-x) is 7/10 iron. So, you want to mix 'em up so that (2/5)x + (7/10)(30-x) = (1/2)(30) x = 20 Check: 20 oz of Alloy 1 contains 8 oz iron 10 oz of Alloy 2 contains 7 oz iron. Total is 15 oz in 30 oz of the mix, or a ratio ...
*April 14, 2016*

**Maths- Calculus**

if you want the volume, that would be, using shells, ∫[0,∞] 2πrh dx where r=x and h=y=e^-x ∫[0,∞] 2πxe^-x dx = -2π(x+1)e^-x [0,∞] = 2π using discs, it is ∫[0,1] πr^2 dy where r = x = -ln(y) ∫[0,1] π(lny)^2...
*April 14, 2016*

**Calculus**

the volume would be ∫[-√5,√5] πr^2 dx where r=y=(5-x^2) Because of symmetry, that is 2∫[0,√5] π(5-x^2)^2 dx = 80π√5/3 using shells, that is 2∫[0,5] 2πrh dy where r=y and h=x=√(5-y) 2∫[0,5] 2πy√...
*April 14, 2016*

**Algebra**

this link is a nice long division calculator: http://calc101.com/webMathematica/long-divide.jsp
*April 14, 2016*

**maths**

Let the total distance be 2d. Then, since time = distance/speed, d/100 + d/90 = 1/3
*April 14, 2016*

**Geometry**

what is the "radius" of a square? Circles have a radius. Squares have a side and a diagonal.
*April 14, 2016*

**Math**

as with all polynomials, it is D
*April 14, 2016*

**Solid Mensuration 04/15/16**

since DE and BC are parallel, triangles ABC and ADE are similar. The ratio of sides of ADE to ABC = 28/70 = 2/5 So, CE = AC * 3/5 = 15 BD = AB * 3/5 = 9
*April 14, 2016*

**math**

what, never done a proof? (C)!
*April 14, 2016*

**maths simultaneous equation**

My previous solution of x=y=z=0 works, but was derived in error. The other solution is x = 5/24 y = 7/24 z = 1/24 x+2y+z = 5xy + 5xz + 5y^2 + 5yz x+y+2z = 7xy + 7xz + 7yz + 7z^2 2x+y+z = 6x^2 + 6xy + 6xz + 6yz Now just start substituting.
*April 14, 2016*

**mathematics-combination vs A.P**

n(n-1)(n-2)(n-3)(n-4)/5! - n(n-1)(n-2)(n-3)/4! = n(n-1)(n-2)(n-3)(n-4)(n-5)/6! - n(n-1)(n-2)(n-3)(n-4)/5! place all over a common denominator of 6! and then you have a polynomial of the 6th degree. Try a few easy values with synthetic division (0,1,2,3) and you can reduce the ...
*April 14, 2016*

**Math**

If he started with $x, then (1/5)(3/8 x) = 60 x = 800 After the spending he had left 800(1 - 5/8 - (1/5)(3/8)) = 240 why do you ask what it means? You presumably are calculating how much was left at the end.
*April 14, 2016*

**math**

http://www.learningace.com/doc/6138186/5b99373c5323a0518f25b611d97ade45/wallis-s-formula-to-integrate-powers-of-sine-or-sine-0-pi-2 is a good place to start. Try adjusting the interval to fit your needs.
*April 14, 2016*

**Calculus 1**

y' = b(1-ax)e^(-ax) 1-ax=0, at x=1/a = 4, making a = 1/4 y(4) = 4be^(-4/4) = 12 4b/e = 12 b = 3e y = 3ex e^(-x/4) verify this at https://www.wolframalpha.com/input/?i=y%3D3ex+e^%28-x%2F4%29
*April 13, 2016*