Saturday
April 30, 2016

Posts by steve

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

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