Friday

December 9, 2016
Total # Posts: 47,015

**calculus**

v = Ï€r^2 h = 10 so, h = 10/(Ï€r^2) The surface area is a = 2Ï€r(r+h) = 2Ï€r(r + 10/(Ï€r^2)) = 2Ï€r^2 + 20/r da/dr = 4Ï€ - 20/r^2 = (4Ï€r^2-20)/r^2 da/dr=0 when 4Ï€r^2=20, or r=â&#...

*November 1, 2016*

**geometry**

if you mean that the center is (4,-1) and (8,2) lies on the circle, then r^2 = (8-4)^2+(2+1)^2 = 25 so the circle is (x-4)^2 + (y+1)^2 = 25

*October 31, 2016*

**brief calc**

a = âˆ«[4,5] 6x dx = 27 or, since the area is just a trapezoid of height 1, a = (24+30)/2 = 27

*October 31, 2016*

**Algebra**

the angles add to 180, so since R=Q+20, Q=R-20 S=Q+115 = (R-20)+115 = R+95 Q+R+S=180 R-20 + R + R+95 = 180 ...

*October 31, 2016*

**Algebra2**

Given no choices, I'd just have to say those closest to the turning points...

*October 31, 2016*

**Algebra2**

Which points are the best approximation of the relative maximum and minimum of the function? f(x)=x^3+3x^2-9x-8

*October 31, 2016*

**Algebra**

2(x + 4x-33) = 104

*October 31, 2016*

**Algebra**

add 9, multiply by 5, divide by -2 and change direction

*October 31, 2016*

**Algebra**

well, just plug and chug: R(x+h)-R(x) ---------------- h

*October 31, 2016*

**Algebra2**

A quadratic equation can be written in vertex form or in standard form. Sometimes one form is more beneficial than the other. Identify which form would be more helpful if you needed to do each task listed below and explain why. a- factor the equation b- graph the parabola c-...

*October 31, 2016*

**Algebra2**

y = -x^2+12x-4 = -(x^2-12x)-4 = -(x^2-12x+36)-4+36 = -(x-6)^2 + 32

*October 31, 2016*

**Algebra2**

What is the vertex form of the equation? Show steps y=-x^2+12x-4

*October 31, 2016*

**Algebra2**

thank you

*October 31, 2016*

**Algebra2**

Complex numbers can be graphed on the xy coordinate plane. TRUE OR FALSE My answer is yes

*October 31, 2016*

**Algebra**

still can't figure out what you mean by pedro works in 3 days and juan in 4 days does that mean that Pedro works for 3 days, and then Juan works for 4 days? It appears that you are saying it takes Pedro 3 days, and it takes Juan 4 days. Then you ask how long it takes each ...

*October 31, 2016*

**plz sir reiny sir steve sir damon help sor bob**

just use the chain rule d/dx arccosh(u) = 1/√(u^2-1) du/dx so, if u = x/√3, that becomes 1/√(x^2/3 - 1) * 1/√3 = 1 / √(x^2-3) since you know that cosh^2(u) = 1+sinh^2(u) d/dx coshu = sinhu, you have y = arccosh(u) coshy = u sinhy y' = 1 y'...

*October 31, 2016*

**math**

600 * 1.04^6

*October 31, 2016*

**maths**

the slope of AB is -1/4 So, the slope of AC is 4 AB has length √68 = 2√17 So, AC has length √17 = √(1^2+4^2) That means that C = A+(1,4) = (2,9)

*October 31, 2016*

**pre algebra PLZZZ help**

what string? and certainly, estimation is often easier than detailed calculation.

*October 31, 2016*

**Pre-Calc/ Trig**

4cos^2(2θ-π) = 3 cos^2(2θ-π) = 3/4 since cos(a-b) = cosa cosb + sina sinb, cos(2θ-π) = -cos(2θ) cos^2(2θ) = 3/4 cos(2θ) = ±√3/2 now cos π/6 = √3/2 so, 2θ = π/6, 5π/6, 7π/6, 11π/6 &#...

*October 31, 2016*

**math**

facing east, of course.

*October 30, 2016*

**MS.SUE PLEASE HELP!!!**

(3/4)(z+8) 6(3x+y) -5(2a+5) in each case, just divide each term by the number you want to factor out.

*October 30, 2016*

**Permutations**

11*10*9 = 990 or 11!/(11-3)! = 11!/8!

*October 30, 2016*

**Algebra II**

just split up the real and imaginary parts, as usual! 19+42i-21yi+28y = (19+28y) + (42-21y)i

*October 30, 2016*

**calculus**

∫√(v^2 sin^2(2π/T t)) dt Looks to me like just ∫|v sin(2π/T t)| dt The absolute value throws in a wrinkle, but the integral is simple enough.

*October 30, 2016*

**Calculus differentiable and continous identify**

For continuous, ya got me. Only F looks like it fails. For differentiable, surely F fails, because it isn't even continuous. Also, (a),(b),(d) fail because of the cusps. I am assuming that d(0) is defined somewhere on the y-axis. (f) fails because the ends of the semi-...

*October 30, 2016*

**Physics 11 steve or any physics teacher helpURGENT**

The total momentum must be conserved. If the boy slides away to the left, the box must move to the right, since momentum is a vector quantity.

*October 30, 2016*

**algebra 2**

If x is the number of years, you need (1 + .038/2)^(2x) = 3000/2000

*October 30, 2016*

**algebra**

80 is 4 half-lives, so at t=0, it was 16 (2^4) times as great.

*October 30, 2016*

**Algebra**

after x years, the value is 14000 * 0.98^x

*October 30, 2016*

**Calculus AB**

#1 f' = (3x+2)e^x since e^x is always positive, just determine where 3x+2 is positive, etc. #2 remember the point-slope form of a line. a) y= x^2 + (e^x)/(x^2 +1) at the point x=3. y' = 2x + (x-1)^2/(x+1)^2 e^x y(3) = 9+e^3/10 y'(3) = 6+e^3/4 So, you want the line ...

*October 30, 2016*

**Math**

type in your functions here, and see whether you can see how to arrive at the solutions. http://www.wolframalpha.com/input/?i=%7C(x-3)%2F2%7C

*October 30, 2016*

**math**

not sure what you have against a simple minus sign, dividion symbols, etc. The rest of us just use simple ascii characters, such as + - / * < <= > >= all are correct except #8 c+6 < -20 c < -26

*October 30, 2016*

**Pre-Calculus**

there are a few standard angles whose exact values we know. By combining them we can get exact values for other angles.

*October 30, 2016*

**Gaussian Elimination Method**

http://www.gregthatcher.com/Mathematics/GaussJordan.aspx

*October 30, 2016*

**maths physics**

Let the three time periods be x,y,z seconds x+y+z = 20 (5/2 x^2) + (5xy) + (5xz-2z^2) = 20 Now, since it decelerates at 4/5 the rate that it took to accelerate, it will take 5/4 as long to come to rest. So, our third equation is z = 5/4 x Now just solve for the time periods, ...

*October 30, 2016*

**physics**

if the angle θ is measured counterclockwise from the +x axis, then the components are x = r cosθ y = r sinθ where r is the magnitude of the directed quantity.

*October 30, 2016*

**maths**

think hypotenuse.

*October 30, 2016*

**math**

see related questions below

*October 30, 2016*

**math**

I suspect a typo. Since they start with the same amount, and the first tank fills more slowly, it will never have more than the second tank.

*October 30, 2016*

**Calculus AB**

why the <note>? Just say what f(x) is. You can use the quotient rule if you want, but note that f(x) = (x-6)/(x+6) = 1 - 12/(x+6) so, f'(x) = 12/(x+6)^2 f'(6) = 12/12^2 = 1/12

*October 30, 2016*

**DISCRETE MATH**

if a_n depends on previous values of the sequence, then it is recursively defined.

*October 30, 2016*

**math- Set**

try using ⊂ for subset (a) ∅ is a subset of all sets. have any thoughts on the others? They really are quite simple.

*October 30, 2016*

**Math 107**

just plug your numbers into the formula, which I'm sure you have.

*October 30, 2016*

**maths**

x = 4/9 x + (4/9 x + 17) x = 153 girls: 68 boys: 85

*October 30, 2016*

**Math**

(10+4)(4+4) - 10*4 (19/16 + 13/4)/(13/4 - 9/16) = 71/43

*October 29, 2016*

**Calculus**

geez, why bother? It's a triangle.

*October 29, 2016*

**Calc**

you don't give an interval, but let's say it's [1,5]. If you use n rectangles, then the upper approximation will use right sums. (Draw the graph and a few rectangles to see why.) n ∑5/(1+k*4/n) k=1

*October 29, 2016*

**maths**

(115+95)km/(1.5+2.5)hr = 210/4 km/hr

*October 29, 2016*

**math**

In QIII you have x = -9 y = -1 r = √82 So, now just recall the definitions of the trig functions for a triangle in standard position.

*October 29, 2016*

**math**

clearly the first digit is 1 or 2 the cubes are 1 and 8 if 10 is a factor, the number ends in 0 start with that, and see where you get.

*October 29, 2016*

**math**

two points on the line or slope and an intercept or a point and the slope or the two intercepts ...

*October 29, 2016*

**Math**

since time = distance/speed, 6/(x-3) = 6/x + 1

*October 29, 2016*

**physics**

PV = kT, so PV/T is constant. So, you want P such that (P)(120)/(40+273) = (1)(140)/(20+273)

*October 29, 2016*

**Math**

use the law of cosines. The angle between the bearings is 35+32 = 67 degrees.

*October 29, 2016*

**math**

6*(2(15+31)-5)

*October 29, 2016*

**Calculus**

Use as many as you want. That's the n. You can estimate the area with a single rectangle, of width pi/2 and height 1, but it won't be a very good estimate. Also, my bad. I was thinking of sin(x) when I mentioned that the estimate was over- or under-. The reverse for ...

*October 29, 2016*

**Calculus**

n ∑(pi/2n)(cos(t*pi/2n) t=1

*October 29, 2016*

**Calculus**

It's a good start. Note that since you are using the right-side sum, and cos(x) is concave down and rising on that interval, the sum will be an upper estimate. Use the left-side sum for a lower estimate. Draw a few rectangles and the curve to see why this is true.

*October 29, 2016*

**Math**

use the law of cosines.

*October 29, 2016*

**1 MATH QUESTION**

the number off coordinates.

*October 29, 2016*

**Math**

see related questions below

*October 29, 2016*

**Trigonometry**

The angle of depression from the top of a lighthouse across the street is 65 degrees. the angle from the lighthouse to what? And across the street from what? All we know is that the lighthouse is 37 tan28° = 19.67 ft taller than the house.

*October 29, 2016*

**Chemistry**

well, velocity = wavelength * frequency

*October 29, 2016*

**Math**

well, 1000 years is 2 half-lives, so ...

*October 29, 2016*

**Algebra 2**

Assuming that sqrt4(125) means ∜125, then A = 3^(1/2) * 5^(3/4) / 7^3 so, logA = (1/2)log3 + (3/4)log5 - 3log7 The base of the logs does not matter. The rules still hold.

*October 29, 2016*

**math**

Recall that for x^2+bx+c the product of the roots is c. If the other root is m, then 4m = k 4+m = 5 Looks like m=1, so k=4 x^2-5x+4 = (x-4)(x-1)

*October 29, 2016*

**Math**

just multiply all the numbers by 2.

*October 29, 2016*

**maths**

start with 1 and 24 Now start increasing the first and decreasing the second till they ass each other. By then you will have listted all the factors.

*October 29, 2016*

**Math**

consider that the amount of sausage never changed. did the solvent remove the fat?

*October 29, 2016*

**Math's**

well, how many oranges in 2 dozen?

*October 29, 2016*

**math**

1.7/B + 1/B = 1/6

*October 29, 2016*

**Maths**

multiply the rows by 3 and 2 and you have 6x-9y = -9 6x-14y = -2 Now subtract to eliminate x, and then y is easy. Use that value of y in either equation to get x.

*October 29, 2016*

**math**

must be all 9's, eh?

*October 29, 2016*

**Math probability**

well, what is the chance that the 1st sock is blue? Having removed it, what is the chance that the 2nd is blue? The number of blues and the number of socks have both been changed by removing the 1st blue sock. Now just multiply.

*October 29, 2016*

**math**

a = F/m, so plug in your numbers.

*October 29, 2016*

**Math Help**

It means the number of elements in the set. Clearly you have not studied your material.

*October 29, 2016*

**Math Help**

so, do you know what n(a) means? If you do, this cannot be a hard problem.

*October 29, 2016*

**math**

ha ha if you can read, just put it into math. If the river's speed is x, then since time = distance/speed, 4/(2+x) = 1/(2-x)

*October 29, 2016*

**math**

google is your friend https://www.quora.com/How-do-you-calculate-the-number-of-squares-in-an-n-x-n-square-grid

*October 28, 2016*

**maybe math**

If Reiny is right, then to simplify, -1/8 + 1/8^2 = -8/8^2 + 1/8^2 = -7/8^2 or, 2 ∑ -2^k/8^2 k=0 How's that for simple? And all positive exponents!

*October 28, 2016*

**Math Derivative**

yes. The good old chain rule. It helps to write them as fractions, so things cancel out: dg/dx = dg/dh * dh/dx I know they usually tell you to avoid thinking of derivatives as fractions, but they really are. It's the same with parametric functions, x(t) and y(t) dy/dx = (...

*October 28, 2016*

**Calculus**

a scalar multiple just distributes as in a complex number: a(x+yi) = ax+ayi (1/2)<-3,7> = <(1/2)(-3),(1/2)(7)>

*October 28, 2016*

**Physics**

conserve total angular momentum.

*October 28, 2016*

**Calculus**

well, y' = -2/(3y), so y" = 2/(3y^2) y' = ...

*October 28, 2016*

**Calculus I**

show what you did. This kind of problem always works out that the fencing is divided equally among lengths and widths. So, the entire array will have dimension (50/3) by (50/4) Each pen will be (50/9) by (50/8) Start with 3x+4y = 100 a = xy = x*(100-3x)/4 then find x such that...

*October 28, 2016*

**Math (Confused)**

9*10^3 * 9*10^4

*October 28, 2016*

**Math (Finding Vertical Tangent)**

looks to me like there is a vertical tangent at x = 2pi/3

*October 28, 2016*

**Algebra**

75% is correct. There is a mistake somewhere in the problem or the answer. Could it be that they won 6 and lost 8? That would make the answer 6/14 instead of 6/8.

*October 28, 2016*

**Chem**

1 mole occupies 22.4L at STP so, you will have 17.8*22.4L PV = nRT

*October 28, 2016*

**Algebra**

cost = revenue to break even So, what is the cost for x pencils?

*October 28, 2016*

**Math**

need for what? and how much is a "dash"?

*October 28, 2016*

**Math**

if x mL were lost and replaced, then .80(250-x) + .40x = .72*250

*October 28, 2016*

**Math - forget it**

Oops - my bad. I misread it. Embershy is correct

*October 28, 2016*

**Math**

23/40 - 23/30 = 23(1/40 - 1/30) = 23(3/120 - 4/120) = 23(-1/120) = -23/120 Note above that 23/30 is not 11/15.

*October 28, 2016*

**Math**

.30*8 + 1.00x = .35(8+x)

*October 28, 2016*

**Chemistry**

The total mass of the solution is x where .0910x = 19.0

*October 28, 2016*

**maths**

660 is nowhere close. You want the circumference of a circle. You don't say whether 220 ft is the diameter or the radius, or even the circumference. If the diameter, your new larger circle has diameter 220+6 = 226 If the radius, your new larger circles has diameter 440+6...

*October 28, 2016*

**easy Math**

well width * length = area so, ...

*October 28, 2016*

**easy math**

(6/2)^2

*October 28, 2016*