Friday

February 12, 2016
Total # Posts: 37,586

**science**

what is the speed of sound at 25°C? If that speed is s, then If the cliff has height, it hits the bottom at time t, where 4.9t^2 = h. So, h = (8-√(h/4.9))*s Plug in your speed s, and find h.
*November 25, 2015*

**math - eh?**

Better read your question. It is gibberish.
*November 25, 2015*

**math**

18 * (32/72) 30 * (8/12)
*November 25, 2015*

**Math**

true, false if x has powers, it is a polynomial. If x is the power, it is an exponential, as in e^x polynomials have constant powers of a variable. exponentials have variable powers of a constant.
*November 25, 2015*

**Pre Calculus**

for any positive real a, y = a^x always goes through (0,1), so y = 4a^x always goes through (0,4) y = a^x + 3 also goes through there. y = h*a^x + k too, if h+k=4 negative powers also work.
*November 25, 2015*

**Algebra**

If x hours at 57 mi/hr, then since distance = speed * time, 57x + 56(4.5-x) = 254
*November 25, 2015*

**Geometry**

yes.
*November 25, 2015*

**Calculus 1**

You can see a nice graph with grid lines here: http://rechneronline.de/function-graphs/ You may have to adjust the y scale some so it fits. You can use that to estimate the area. I'm sure you can then evaluate the integral.
*November 25, 2015*

**derivatives**

is that (cos t)^2 or cos(t^2) ? Then express t as functions of x and y, and you have dy/dx = (dt/dx) / (dt/dy) then you can use that to get the 2nd derivative
*November 25, 2015*

**electron theory and ohms law**

ummm. E = IR ? This time find I.
*November 25, 2015*

**electron theory and ohms law**

E = IR = 6.4 * 20
*November 25, 2015*

**math**

average cost is (1/3 x^3 – 18x^2 + 160x)/x = 1/3 x^2 - 18x + 160 marginal cost is x^2-26x+160 so, where is 1/3 x^2 - 18x = x^2 - 26x ?
*November 25, 2015*

**Algebra II, part 2**

#6. Surely by now you can do this... #7. b^2-4ac = 9+4*2*18 #8. 3√-3 = 3√3 i #9. Multiply top and bottom by conjugate: 8(3-2i)/13
*November 24, 2015*

**Algebra II**

#1. x^2 has negative coefficient. downward #2. (5/2)^2 #3. hint: 15+1 = 16 #4. does not factor. Did you mean +2x? #5. shift left 2, scale vertically by 1/3, shift up 5
*November 24, 2015*

**algebra 2**

Well, I see 2x^2+3x+1 and 3ay^2+9a If you want to factor them, then you have (2x+1)(x+1) and 3a(y^2+3) Other than that, I'm not sure what you want to do with them.
*November 24, 2015*

**Trigonometry**

#1. no calculator? It will be in 1st quadrant. #2. how long is the court? The angle is x where tan(x) = 2.44/(court length)
*November 24, 2015*

**Math**

so, if the width is w, 2(w + 2w) = 126
*November 24, 2015*

**Algebra 2**

y = (x-10)(x-4) I expect you can take it from there, no?
*November 24, 2015*

**Math**

yep.
*November 24, 2015*

**Math**

the range is the set of 2nd elements of the pairs.
*November 24, 2015*

**Calculus III**

Looks ok to me
*November 24, 2015*

**Physics**

F = ma = 80kg * 9.8 m/s^2 W = Fd = F * 6m P = W/s = W / 15s P = 80*9.8*6/15 = 313.6 W Now you can figure the % eff.
*November 24, 2015*

**MacArthur physics**

height: s = 4.9t^2 speed: 9.8t range: 20t
*November 24, 2015*

**Math**

cool. nice and wavy.
*November 24, 2015*

**arvind mahila college**

T7/T4 = r^3 = (8/9)/3 = 8/27 so, r = 2/3 Now you can find the 1st term and thus whatever terms you want.
*November 24, 2015*

**Algebra**

Been there, done that. http://www.jiskha.com/display.cgi?id=1448344846
*November 24, 2015*

**Math**

well, what is 3 cows plus 6 cows? 3 doughnuts plus 3 doughnuts? whatever x is, you have 3+3 of it.
*November 24, 2015*

**math**

c(x) = 3 + x/3000 + e^(-.003x) c'(x) = 1/3000 - .003e^(-.003x) So, you can see that the cost to produce a unit consists of a fixed amount, plus a steadily decreasing variable amount as more are produced. That means that the cost of the 100th unit is c'(100) = 1/3000...
*November 24, 2015*

**Algebra 1**

without knowing step 4, it's hard to say. Both distributive and associative properties are expressed. I doubt very much that it is a fact, as it's just an expression, with no assertion that it is true.
*November 24, 2015*

**Math,Mensuration**

just plug in your numbers: S = 2πr(r+h) V = πr^2 h
*November 24, 2015*

**math**

If the length is x, then the width is x-4. So, the perimeter is 2(x + x-4) = 56
*November 24, 2015*

**college algebra**

Assuming you meant a bicycle tire makes 3 complete revolutions for each revolution of the pedal then we have (in inches/minute) 100 * 3 * 27π Now just convert that to miles/hour.
*November 24, 2015*

**math**

base = s/2 leg = 2s s/2 + 2*2s + 4s = 34 Now solve for s, and then the triangle's sides.
*November 24, 2015*

**Algebra**

since time = distance/speed, 20/(x-3) + 20/(x+3) = 5
*November 24, 2015*

**Algebra**

just solve t^2-2t = 48 t^2-2t-48 = 0 (t-8)(t+6) = 0 I expect you can take it from there, no?
*November 24, 2015*

**Math**

multiply by -3
*November 24, 2015*

**math**

review the definition of cot(x). You will see that if the height is h, h*cot27° - h*cot29° = 1000
*November 24, 2015*

**Maths**

x+y = 32 4x-5 = 8y Solve for x and y, then x-y
*November 24, 2015*

**Algebra**

If x at 5%, y at 10%, then 200+x+y at 15% x+y+200+x+y = 7000 .05x + .10y + .15(200+x+y) = 815 Now just solve for x and y, and then x+y+200
*November 24, 2015*

**math (check answers)**

looks good to me. nice work.
*November 24, 2015*

**math**

so, do you mean ln(xy-sqrt(x^2-y^2)) or ln(xy)-sqrt(x^2-y^2) I will assume the first, since the 2nd is much easier ∂z/∂x = 1/ln(xy-√(x^2-y^2)) * (y-x/√(x^2-y^2)) and similarly for y.
*November 23, 2015*

**math**

you can use the techniques discussed here http://math.stackexchange.com/questions/783469/evaluate-the-limit-with-taylor-series to break it into pieces, and use the Taylor series to evaluate using the linearity of limits. Each function involved has a relatively easy-to-get series.
*November 23, 2015*

**Physics**

(30 m/s)/(5s) = 30/5 = 6 m/s^2
*November 23, 2015*

**Physics**

(25-15) m/s ------------------ = 2 s 5 m/s^2
*November 23, 2015*

**TECH MATH**

the volume of a cylindrical hole in a sphere is discussed here: http://mathworld.wolfram.com/SphericalRing.html Just plug in your numbers.
*November 23, 2015*

**math**

since 9=3^2, log_3(9^12) = log_3(3^24) = 24 Not quite sure what 9logexponent 12 means.
*November 23, 2015*

**MATH**

6. 60/45 = 4/3 = 12/9 7. (a) 200cents/64floz = 3.125 cents/floz You can do (b) the same way and then compare for (c) 8. 3/10 in = 7/8 mi (3/10)(8/7)in = 1 mi
*November 23, 2015*

**math**

since a sample of 20 contained 13, a bag of 5*20 should contain 5*13
*November 23, 2015*

**calculus**

assuming the usual sloppiness, we have y=(5x^2-45)/(x^2-25) y'= -160x/(x^2-25)^2 y" = 160(3x^2+25)/(x^2-25)^3 since y" is never zero, there are no inflection points, as can be confirmed here: http://www.wolframalpha.com/input/?i=%285x^2-45%29%2F%28x^2-25%29
*November 23, 2015*

**Math**

I guess you are. It is on the line between QII and QIII.
*November 23, 2015*

**Math**

If the lowest and highest are x and y, then we have, adding up all the points: x+5*78+y = 80*7 x+y = 560-390 = 170 (x+y)/2 = 85
*November 23, 2015*

**math**

If he sold x shares, then he'd have made .0214x By selling them, he received 77x Investing them, he bought 77x/100 shares of 6% shares. 77x/100 * .06 = .0462x So, he increased his income by (.0462-.0214)x = 117 x = Rs 4717.74 If the slow pipe takes x minutes, then we have ...
*November 23, 2015*

**Calculus - typo**

or, (-1/r) e^[(-1/r) t] since d/dt e^(kt) = ke^(kt)
*November 23, 2015*

**College Alg.**

If the amounts in A and B are x and y, then (suppressing all the extra zeros), maximize p=.13x+.07y subject to x >= 65/2 y >= 65/4 x+y <= 65 Now use your favorite tool to solve. A good one is at http://www.zweigmedia.com/RealWorld/LPGrapher/lpg.html
*November 23, 2015*

**Math**

Jiskha and facebook
*November 23, 2015*

**Geometry**

well, the side lengths are CB=10 Note that A is halfway from C to B (6=(1+11)/2), so ABC is an isosceles triangle, and AB=AC=√74 Now all you have to do is scale up the dimensions by a factor of 20'/1" = 240 to get the actual side lengths. We weren't asked ...
*November 23, 2015*

**Geometry - incomplete**

I assume you meant ACB rather than ACV. Since the angles total to 180, we have for angle ABC, 180-(5x+1)-(3x+12.5) = 162.5-8x That is all we know. You have given no side lengths, nor even any way to determine the actual angles. Knowing all the angles would not help, since we ...
*November 23, 2015*

**math**

10+16 = ?
*November 23, 2015*

**math**

2L/5child = 2/5 L/child
*November 23, 2015*

**math**

well, just add 'em up and divide by 5. The numbers are 36,49,64,81,100
*November 23, 2015*

**math**

y = x^x^x^... lny = x^x^x^... lnx = y lnx lny/y = lnx Now differentiating implicitly, 1/y y' - lny/y^2 y' = 1/x y' = (1/xy)/(1 - lny/y) You can massage that in various ways.
*November 23, 2015*

**Calculus**

I think we can safely assume that the max volume occurs when h+r is in fact 12, and not less. So, h = 12-r v = πr^2 h = πr^2(12-r) dv/dr = 3πr(8-r) So, max v occurs at r=8 v(8) = π*8^2(4) = 256π I think you can easily show that if h < 12-r, max v ...
*November 23, 2015*

**Maths**

the dimensions of the box are x,x,y where x^2 y = 2592, so y = 2592/x^2 Around the square, the distance is 4x Around the length, the distance is 2x+2y So, we want the minimum length. No maximum is possible, as the package may be arbitrarily long and thin. So, the length z is z...
*November 23, 2015*

**Calculus**

f' = 9x^(4/5) - 36/x^(1/5) = 9/x^(1/5) (x-4) f increases where f' > 0, or x>4 or, where x<0
*November 23, 2015*

**Math**

f' = x (lnx)^2 f" = lnx(lnx+2) f is concave down where f" < 0, or -2 < lnx < 0 That is, on the interval (1/e^2,1) You can see the graph of f(x) at http://www.wolframalpha.com/input/?i=1%2F4+x^2+%282%28lnx%29^2-2lnx%2B1%29+for+0%3Cx%3C2
*November 23, 2015*

**math**

height = 26 sin75° base is 26 cos75° feet from wall
*November 22, 2015*

**Pre-Algebra**

solve for t where 6 + 46t - 16t^2 = 39
*November 22, 2015*

**math**

4.50x + 5.50*20 = 5.00(x+20)
*November 22, 2015*

**Math**

35*.70 + 45*.30 = ?
*November 22, 2015*

**physics**

If the car stops in t seconds, the deceleration a is 35.5/t The distance traveled is s(t) = 35.5t - (35.5/2t)t^2 = 52.7 so, t = 2.97 seconds. a = 35.5/2.97 = 11.953 m/s^2 F = ma = 2165.7 * 11.953 = 25,886 N
*November 22, 2015*

**math**

(b+B)/2 * 2 = 36 b+B = 36 4x+5x=36 x=4 The bases are 16 and 20
*November 22, 2015*

**Physics IB**

see related questions below.
*November 22, 2015*

**Math**

if they are dependent they are the same line. So, the solution set is all real numbers. Any solution to one equation is a solution to the other.
*November 22, 2015*

**Calculus**

you have ∫[-∞,+∞] (x-μ)^2 1/r e^-(x/r) dx This just boils down to ∫x^2 e^(-x) dx with suitable constants thrown about. Do it with integration by parts twice to get -(x^2+2x+2)e^(-x) Now substitute in (x-μ) and x/r and things work out ok.
*November 22, 2015*

**Algebra**

If it takes him x hours, then 1/9 + 1/x = 1/5
*November 21, 2015*

**trigo**

You want <x,y> such that <x,y> + <0,-45> = <20,0> clearly that is <20,45> Now just convert that to speed and direction.
*November 21, 2015*

**wcccd**

looks like a good description...
*November 21, 2015*

**math**

original area: (x)(x) = x^2 larger area: (2x)(2x) = 4x^2 area goes up as the square of the scale factor, because both dimensions are multiplied. BTW, did you actually draw the squares? The answer would have been clear.
*November 21, 2015*

**Calculus**

and watch out for that "c"
*November 21, 2015*

**Science**

clearly, 2/3 mole NH3. So, just convert that to grams.
*November 21, 2015*

**Calculus**

∫[0,∞] xe^-x dx = -(x+1)e^-x [0,∞] lim -xe^-x = 0 x->∞ by lHospital's Rule so, ...
*November 21, 2015*

**College Algebra**

consider 4000 pieces one "job". The classic work problem now becomes 1/5 + 1/x = 1/3 x = 15/2 So, he can sort 2000 mails (1/2 job) in 15/4 hour
*November 21, 2015*

**Maths**

y = (x^2+5x^7)/x y = x + 5x^6 y' = 1 + 30x^5
*November 21, 2015*

**Math**

assuming base 3, log((4x+1)(13x-5)) = 2 (4x+1)(13x-5) = 3^2 = 9 52x^2 - 7x - 5 = 9 Now just solve the quadratic
*November 21, 2015*

**math**

total money = x .10*0.80x*2 - r*0.20x*2 = 3300 Without knowing x, there is no way to determine .10-r
*November 21, 2015*

**mathematics**

draw each line. Then shade the area below the two slanting lines, above the x-axis, and between the y-axis and the vertical line at x=80. The solution is the part where all the shaded areas intersect. A good start is shown here: http://www.wolframalpha.com/input/?i=solve+3x%...
*November 21, 2015*

**interes rate**

(1+r)^16 = 2 Now just solve for r.
*November 21, 2015*

**math**

x+y = 120, so y = 120-x z = x^2y = x^2(120-x) dz/dx = 240x - 3x^2 = 3x(80-x) absolute maximum of x^2y is at x=80 so, x=80, y=40 Note that this is very like the fencing problems, where the length is divided equally among the lengths and widths. Here, the powers of x and y are ...
*November 21, 2015*

**Calculus**

dz/dt = 2t e^z e^-z dz = 2t dt -e^-z = t^2 + c e^-z = c-t^2 -z = ln(c-t^2) z = -ln(c-t^2) at(0,0) 0 = -ln(c) c = 1 z = -ln(1-t^2) I like your answer. Maybe they want z = ln(1/(1-t^2))
*November 20, 2015*

**Calculus**

Hmmm. I get y = -e^(x/2) - 7e^(-3x) Better check your algebra. 2t^2+5t-3 = (2t-1)(t+3)
*November 20, 2015*

**World History**

thank you
*November 20, 2015*

**World History**

Sorry my answer is d
*November 20, 2015*

**World History**

Leaders in the industrialized world see booming populations in the least industrialized nations as a threat to? a= the continued expansion of their own nations b= technologymadvancement c= the global balance of power d= the existing food supply
*November 20, 2015*

**Math**

because one solution will lie on the positive real axis. The rest are evenly spaced above and below that axis, giving conjugate pairs.
*November 20, 2015*

**math**

He finds mc022-1.jpg and mc022-2.jpg.
*November 20, 2015*

**math**

If the depth is x dm, then we have 48*31.5*6.5 = 27*18.2*x If his speed is x in still water then 12/(x-4) = 5 Use that x to evaluate 15/(x+4) Draw a diagram. If you draw a radius perpendicular to the chords, you bisect them. You then have two 3-4-5 triangles (the radius of 5 ...
*November 20, 2015*

**trigonometry**

r = 7cos(θ+π/4) r^2 = 7rcos(θ+π/4) x^2+y^2 = 7/√2 r(cosθ-sinθ) x^2+y^2 = 7/√2 (x-y) You can massage that into the standard circle form if you want. Or, cheat here: http://www.wolframalpha.com/input/?i=x^2%2By^2+%3D+7%2F%E2%88%9A2+%28x-...
*November 20, 2015*

**conversions**

of course, the gauge does not matter for area. So, you have 30500 ft * 1m/3.28ft * 117in * 1ft/12in * 1m/3.28ft = 27640 m^2
*November 20, 2015*

**Maths**

it's just a flat line of any length. That is, its altitude is zero. Or, maybe it has an altitude, but a zero-length base, so it's a vertical line.
*November 20, 2015*

**physics**

huh? It does. Ever seen moist soil after a hot afternoon?
*November 20, 2015*