Friday
February 12, 2016

Posts by Steve

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

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