Saturday

March 28, 2015

March 28, 2015

Total # Posts: 30,131

**math**

a gallon is 16 cups so, the concentrate is 2/18 = 1/9 of the total volume. so, what is 1/9 of 16 fl oz?
*March 4, 2015*

**statistics/normal distribution**

you can play around a lot with Z table stuff here: http://davidmlane.com/hyperstat/z_table.html
*March 4, 2015*

**math**

(30*15*20 - 30*15*15)/5^3 = 18
*March 4, 2015*

**Geometry**

if x is line-of-sight, 8000/x = sin 40° if x is along the ground, 8000/x = tan 40°
*March 4, 2015*

**math**

nope. odd+odd+odd = odd
*March 4, 2015*

**Math**

If the I were a T, the word would be CONGRUENT Sure there's no typo?
*March 4, 2015*

**Math**

using the law of sines, if A is x miles away, and B is y miles away, x/sin10° = y/sin60° = 17/sin110° Now you can find x and y, and thus y-x.
*March 4, 2015*

**Math**

use the law of cosines x^2 = (13*40)^2 + (10*30)^2 - 2(13*40)(10*30) cos 135°
*March 4, 2015*

**math**

use the law of cosines. x^2 = 3^2 + 4^2 - 2(3)(4) cos 45°
*March 4, 2015*

**math**

cannot be done. three odd numbers will always add to an odd result.
*March 4, 2015*

**math**

If the circle is tangent to both axes, you know its center is on the line y=x. So, now you know that the center is at the intersection of the two lines: (2,2) So, the circle has radius 2, and is (x-2)^2 + (y-2)^2 = 4 See the graphs at http://www.wolframalpha.com/input/?i=plot...
*March 4, 2015*

**math**

f + (2f-5) + (2/3)f = 28
*March 4, 2015*

**calculus**

y = 2^(3x^2) y' = ln2 * 6x * 2^(3x^2) it helps to go at it like this y = 2^(3x^2) ln y = 3x^2 ln2 1/y y' = 6x ln2 y' = ln2 6x 2^(3x^2)
*March 4, 2015*

**mathematics function**

25-x^2 -x^3 e^-x cos(x/4) coth -1 x lots of possibilities
*March 4, 2015*

**algebra**

y-63 = (57-63)/(5-3) (x-3)
*March 4, 2015*

**Algebra 1**

must have done since 3x+y = -9, -3x = y+9 using that, we have (y+9)-2y = 12 -y = 3 y = -3 It would have helped had you shown your work.
*March 4, 2015*

**Algebra 1**

-3(3)+ 1= -9+1 = -8 you are correct
*March 4, 2015*

**math**

easy - just make sure the changes in y are not a multiple of the changes in x. x: 0 1 2 3 4 5 y: 1 3 -99 20 31 22 In fact, almost any six pairs you choose will likely not be a linear relationship.
*March 4, 2015*

**math**

y decreases by 5 as x increases by 1, so look for a rule like y = -5x Since y(0) = -1, y = -5x-1
*March 4, 2015*

**Calculus 1**

do this one just like the other one I worked out.
*March 4, 2015*

**Calculus 1**

see the post below for the way to get this done.
*March 4, 2015*

**Calculus 1**

y = 6/(1+e^-x) = 6e^x/(1+e^x) y' = 6e^x/(1+e^x)^2 so, at (0,3) the slope is 3/2 Now you have a point and a slope, so the line is y-3 = 3/2 (x-0) see the graphs at http://www.wolframalpha.com/input/?i=plot+y%3D+6%2F%281%2Be^-x%29%2C+y%3D3%2F2+x%2B3
*March 4, 2015*

**general maths**

since all the numbers are odd, there is no way adding three of them can give an even result.
*March 4, 2015*

**math**

take a look at a chessboard. There are at least two ways to figure it out.
*March 4, 2015*

**Physics**

Energy Budget for a Rocket in Free Space: Recall the analysis of the rocket engine in Project I, Flight of the Rocket. Although the momentum of the rocket and its exhaust is conserved (constant), their energy is not; energy must be supplied by the combustion of fuel. WARNING: ...
*March 4, 2015*

**immaculate college**

assuming you mean (2 sin(A/2))^2 = 2 4 sin^2(A/2) = 2 sin^2(A/2) = 1/2 sin(A/2) = ±1/√2 Now just find all the angles that fit that.
*March 4, 2015*

**Math**

volume is length * width * thickness
*March 4, 2015*

**math**

The smallest circle has a radius of 2. Each circle's radius is 3/2 that of the previous one. If there are n circles, then since the first and last circles are only traversed halfway, we have 2 + 4(3/2) + 4(3/2)^2 + ... + 2(3/2)^(n-1) = 665/8 Hmmm. I get a non-integer ...
*March 4, 2015*

**math**

looks good to me.
*March 4, 2015*

**math**

since all the digits are less than 5, just lop off the last 4 digits and replace them with zeros.
*March 3, 2015*

**calculus**

y = ln(x-√(x^2-1)) y' = 1/x-√(x^2-1) * (1-x/√(x^2-1)) = -1/√(x^2-1) so, the arc length is ∫[1,√2] √(1+y'^2) dx = ∫[1,√2] √(1+1/(x^2-1)) dx = ∫[1,√2] x/√(x^2-1) dx . . .
*March 3, 2015*

**Physics**

Energy Budget for a Rocket in Free Space: Recall the analysis of the rocket engine in Project I, Flight of the Rocket. Although the momentum of the rocket and its exhaust is conserved (constant), their energy is not; energy must be supplied by the combustion of fuel. WARNING: ...
*March 3, 2015*

**math**

10(6+2r) = 60+20r
*March 3, 2015*

**calculus**

a = pi d^2 da/dt = 2pi d dd/dt You have da/dt and d, so find dd/dt
*March 3, 2015*

**math**

2.60 + mg = 60.0 The weight is mg, so . . .
*February 28, 2015*

**Math**

If the terms were 2,4,6,8,10 could you do it?
*February 28, 2015*

**Math**

count the tablets and the ingredients: a + b + c = 225 12a + 17b + 22c = 4075 10a + 13b + 35c = 4975 Now just use your matrix tools.
*February 28, 2015*

**Vectors**

Just set up your determinants, and you will see how it works. If you multiply any row of a determinant by k, the value also is multiplied by k.
*February 28, 2015*

**ap calc**

Well, if you graph things, you have a curved triangular region with vertices at (-2,8),(-2,0),(0,0). So, using shells of thickness dx, you have the area as ∫[-2,0] 2πrh dx where r = 1-x h = y = -x^3 using washers of thickness dy, you have ∫[0,8] π(R^2-r^2...
*February 28, 2015*

**ap calc**

I think you have a typo. The given curve and lines do not enclose an area. Do you mean x=0. The parabola does not cross y=0 anywhere.
*February 28, 2015*

**calculus**

Those two curves do not enclose an area.
*February 28, 2015*

**math**

well, the only choices are 64 and 10 - nope 49 and 15 - nope 36 and 36 - yep 6+6=12 6^2+6^2 = 72
*February 28, 2015*

**math**

you can use the quadratic formula, and mess with all those fractions, or you can see that you really have 1/12 (12x^2-x-1) = 1/12 (4x+1)(3x-1) Now the roots become clear.
*February 28, 2015*

**calculus**

The curves intersect at (0,0) and (2,2) So, you can add up horizontal strips or vertical strips. In this case, vertical strips are easier (why?) a = ∫[0,2] (2x-x^2) dx = 4/3
*February 28, 2015*

**Health**

Does a diet will help you lose 10 pounds in 3 days debunk the nutrition myth? My answer is yes
*February 28, 2015*

**calculus**

the extrema occur where f' = 0 So, where do you have 9-4x^2 = 0? With those values, you can evaluate the integral to find the value of f(x) there
*February 28, 2015*

**math**

two complementary angles add up to 90. So, what do you have to add to 42 to get 90?
*February 27, 2015*

**math vectors**

come on. You can do a cross product, right? So, pick some vectors and do the math. For example, let u = <1,1,1> v = <1,-1,1> w = <2,1,3> (uxv)xw = <2,0,-2>x<2,1,3> = <2,-10,2> ux(vxw) = <1,1,1>x<2,-1,3> = <4,-1,-3>
*February 27, 2015*

**Algebra**

actually, as written, the equation is not true, but we'll let that go. When you divide by fractions, you invert and multiply: (a/b) / (c/d) = (a/b)(d/c) = ad/bc So, you have (x^2-1/x^2-9)(x^2+8x+15/x^2+3x-4) Now just factor everybody and start cancelling: (x-1)(x+1)(x+3)(x...
*February 27, 2015*

**Geometry**

If P = (x,y), then we have the two transformations (x,y) -> (x+2,y-2) -> (2-y,-(x+2)) so, 2-y = 2; y=0 -(x+2) = 6; x = -8 Hmmm. no luck. If we reflect first, then we have (x,y) -> (-y,-x) -> (-y+2,-x-2) so, -y+2 = 2; y=0 -x-2 = 6; x = -4 Looks like D to me. You ...
*February 27, 2015*

**Math vectors**

the point is, that any numbers will produce zero. You just have to remember that the cross product distributes: (a+b)x(a+b) = axa + bxa + axb + bxb since axa = bxb = 0 and axb = -bxa the sum is zero.
*February 27, 2015*

**Science**

This problem is poorly presented in so many ways. trains don't travel with a force, but rather a speed. If the speed is constant, then the net force is zero. When the conductor applies the brakes with a force of 500N, is that the force of his foot on the control, or the ...
*February 27, 2015*

**math**

3/5 * 1/12 = 1/20
*February 27, 2015*

**math**

he spent 7/9, so 2.50 is 2/9 of the original amount 2/9 x = 2.50
*February 27, 2015*

**algebra**

huh? how complicated can it be to plot four points and connect them?
*February 27, 2015*

**trig**

all reference angles are relative to the x-axis. So, add or subtract π until you get a value in the range [-π/2,π/2] 11π/6 = 2π - π/6 so, the reference angle is π/6
*February 27, 2015*

**Pre-calculus (Trigonometry)**

the ship is 500 sin 20° = 171 m from shore. A beam of 250m will illuminate 2√(250^2-171^2) = 365 m of shoreline.
*February 27, 2015*

**3rd grade math**

I know. Maybe one of the band members is not a musician, eh? Probably the drummer. :-)
*February 26, 2015*

**3rd grade math**

since 3 does not divide 16, how can 2/3 of the 16 players be girls? 12/16 are brass
*February 26, 2015*

**algebra**

1695/(x + x+65) = 3
*February 26, 2015*

**Math**

v = 1/3 πr^2h 3v = πr^2 h h = 3v/(πr^2)
*February 26, 2015*

**math**

61.4% is the amount paid. That is not the discount (which is the amount not paid)
*February 26, 2015*

**Geometry**

90° is 1/4 of a circle. So, what's 1/4 of the circumference or area? c = πd, so d = c/π c = 2πr, so r = c/2π a = πr^2 = π*(c/2π)^2 = c^2/4π Now just plug in c where you need it.
*February 26, 2015*

**math**

not quite If they start out with o and c dollars, then o-40 = c+40 4(c-80) = o+80 rearrange things a bit and you have o-c = 80 o-4c = -400 3c = 480 c = 160 now find o
*February 26, 2015*

**Algebra II**

a parabola with focus at (0,p) and directrix at y = -p is x^2 = 4py The vertex is midway between the focus and directrix, so your parabola has p = 1 x^2 = 4y Now shift things so the vertex is at (-2,5) and you have (x+2)^2 = 4(y-5)
*February 26, 2015*

**math**

since Mickey had only gone 5/6 of the way, Dylan's speed was 6/5 of his. The last 1/6 (40 mi) of the trip took Mickey 48 minutes. That should get you started.
*February 26, 2015*

**Math**

you want to find factors of 81. They are 1,81 3,27 9,9 Each choice gives a different perimeter.
*February 26, 2015*

**math**

210/35 + 54/18
*February 26, 2015*

**Quick chemistry help**

each molecule is Cl2.
*February 26, 2015*

**math**

(5000-600)/4 grams per book
*February 26, 2015*

**math proportions**

since the ratio of height:shadow is constant, 5'1"/3'4" = h/12'10" That's kind of messy, so convert all the values to just inches. Find h, then convert it back to feet&inches.
*February 26, 2015*

**Math**

(a) is clearly explained at http://tinypic.com/view.php?pic=15qynhv&s=4#.VO_LNywYFvA You can probably find the others as well. Usually the Binomial Theorem is involved. For instance, (b) f(x+h) - f(x) = (x+h)^4 - x^4 = x^4+4x^3h+6x^2h^2+4xh^3+h^4 - x^4 = 4x^3h+6x^2h^2+4xh^3+h^...
*February 26, 2015*

**Math vectors**

recall that one factor in the result is the sine of the angle between the vectors.
*February 26, 2015*

**Math/Solve**

correct
*February 26, 2015*

**algebra**

x+y = 70 y = 2x+10 Now go for it.
*February 26, 2015*

**Math**

If the costs are x,y,z, respectively, then we have 2x+2y+z = 10.20 x = 2y z = x+3 You want to find z.
*February 26, 2015*

**linear algebra**

(a) Nope if f(t) >= 0 but c < 0, cf(t) is not a nonnegative function Looks to me like (b) and (c) are both subspaces. Do we have to choose only one?
*February 26, 2015*

**algebra**

3x means he withdrew x dollars each week. You want x to be the starting amount, so x - 3*14 > 65
*February 26, 2015*

**Calculus**

d/dx e^u = e^u du/dx
*February 26, 2015*

**Calculus**

well, y' = 4x^3 + 8x - 1 So, at (1,4), the slope of the tangent is 11. That means the line there is y-4 = 11(x-1)
*February 26, 2015*

**Calculus**

when a is a constant, g'(au) = a g' You know that if y=2x, y'=2(1) y=3x^7, y' = 3(7x^6) The constant is just a multiplier, and carries through. So, what you have is g = √2 u + √7√u
*February 26, 2015*

**math**

you need more than just the scale.
*February 26, 2015*

**Math**

the time in the air is t when h=0 again. So, just solve for h(t) = 0. the max height is the vertex of the parabola, clearly when t=4.
*February 26, 2015*

**math**

y = x/3 + 7 now just plug in x=18 and evaluate for y.
*February 26, 2015*

**Math**

You found the union, not the intersection. 3.3: You found A-B, not the union. 4.4: Again, you found the union. The intersection is the elements in all three sets: {1,5}
*February 26, 2015*

**math**

one recall that the roots are -b/2a ±√(discriminant) so, if the discriminant is zero, both roots are -b/2a
*February 26, 2015*

**math**

the lateral surface area is just the circumference times the height. So, a = 4*15 = 60 if you have to include the ends, then that is additional 2πr^2, where r = 4/2π
*February 26, 2015*

**MATH**

graphing the other methods are exact.
*February 26, 2015*

**Math**

(2/5)(1/5) + (3/5)(1/3)
*February 26, 2015*

**math**

there are several similar problems in the related questions below.
*February 26, 2015*

**Math!! Help ASAP**

11.4 is correct.
*February 26, 2015*

**maths**

3 5/9 = 32/9 40 1/2 = 81/2 So, the common ratio, r^6 = (32/9)/(81/2) = 64/729 r = 2/3 T5 = 32/9 * (2/3)^4
*February 26, 2015*

**maths**

ar = a+4 ar^2 = ar+9 Now just solve for a and r
*February 26, 2015*

**calculus**

no ideas on any of the questions? They gave you the function, so things should just fall right out.
*February 26, 2015*

**math**

y = (x^4+4)^2 (x^3+4)^4 ln y = 2ln(x^4+4) + 4ln(x^3+4) 1/y y' = 8x^3/(x^4+4) + 12x^2/(x^3+4) y' = [8x^3/(x^4+4) + 12x^2/(x^3+4)]*[(x^4+4)^2 (x^3+4)^4] Now you can massage that as you will. Eventually you can arrive at y' = 4x^2 (x^3+4)^3 (x^4+4) (5x^2+8x+12)
*February 26, 2015*

**Math**

By "side" I assume you mean one of the bases. If the other base is x, then we have (6+x)/2 * 13 = 91 (6+x)/2 = 7 6+x = 14 x = 8
*February 26, 2015*

**programming**

as usual, the average is the sum of all the ages, divided by the number of pupils. Count the pupils as they come in: num_pupils = sum_of_ages = 0 loop { read in years, months num_pupils++ age_in_months = years*12 + months sum_of_ages += age_in_months } average_age = ...
*February 26, 2015*

**math**

see related questions below
*February 26, 2015*

**maths**

the values are 1/√3, 1, √3, ... I think you can see what the constant ratio is.
*February 26, 2015*

**arithmetic**

the sides of such a hexagon are the same as the radius of the circle.
*February 26, 2015*

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