Sunday

October 4, 2015
Total # Posts: 34,238

**math**

clearly, after t hours, the population is 2^t. So, when is 2^t = 3?
*October 4, 2015*

**Algebra**

sides are 4x,x,x perimeter is 6x the desired ratio is x/6x = 1/6
*October 4, 2015*

**calculus**

ever heard of the product rule? f = 5e^x cosx f' = 5e^x cosx - 5e^x sinx = 5e^x (cosx - sinx) f" = 5e^x (cosx - sinx) + 5e^x(-sinx-cosx) = -10e^x sinx
*October 4, 2015*

** Chem**

copper sulfate reacts with sodium hydroxide producing copper hydroxide and sodium sulfate.. If sodium hydroxide is the limiting agent how many grams of copper hydroxide should precipitate out?{There are 634.44 g of copper sulfate and 240 grams of sodium hydroxide.
*October 3, 2015*

**college algebra math help**

just use the quadratic formula, as usual.
*October 3, 2015*

**Math**

right on.
*October 3, 2015*

**calculus i need help also**

assuming you meant y = 2x^3-21x^2+60x+6 y' = 6x^2-42x+60 y" = 12x-42 y"=0 when x = 7/2 For the other one, (x^1/2+x^1/3)dx = 0 ∫(x^1/2+x^1/3)dx = C 2/3 x^(3/2) + 3/4 x^(4/3) = C at x=1, C = 2/3 + 3/4 = 17/12
*October 3, 2015*

**calculus need help**

not even sure what a "differencial coefficient" is Do you mean to find the derivative, using the definition as a limit?
*October 3, 2015*

**Algebra**

using the two-point form, we have y-1 = (-3-1)/(9+3) (x+3) Now simplify and put into standard form.
*October 3, 2015*

**Chemistry**

copper sulfate reacts with sodium hydroxide producing copper hydroxide and sodium sulfate.. If sodium hydroxide is the limiting agent how many grams of copper hydroxide should precipitate out?
*October 3, 2015*

**Calculus**

C(R) = .20R C(x) = .20(70x) The notation shown is confusing, since x is used for two different things.
*October 3, 2015*

**science**

position is measured in meters. Its change in time is velocity, m/s velocity's change in time is acceleration: (m/s)/s = m/s^2
*October 3, 2015*

**science**

well, since p = mv, just do the math...
*October 3, 2015*

**Integration need help also**

To make things a bit clearer, ∫sin(x^2) x dx let u = x^2 du = 2x dx and you have ∫1/2 sin(u) du not so hard, eh?
*October 3, 2015*

**@Reiny**

That's my favorite theorem! Too bad it's not taught more. In all fairness, when you're brand new at this stuff, things often seem more confusing than they are. The main problem I encounter is that students seem to forget what the exercise set covers. If you've ...
*October 3, 2015*

**Maths**

look at the remainders when dividing powers of 2 by 13: n 2^n mod13 0 1 1 1 2 2 2 4 4 3 8 8 4 16 3 5 32 6 6 64 12 7 128 11 8 256 9 9 512 5 10 1024 10 11 2048 7 12 4096 1 ... so, you see that 2^n mod 13 = 2^(n+12) mod 13 2011 = 167*12 + 7 so, 2^2011 mod 13 = 2^7 mod 13 = 11
*October 3, 2015*

**Physics**

ever see a 5-12-13 right triangle?
*October 3, 2015*

**Maths**

If the smaller plot has width w, then w*7w = 1250/5 7w^2 = 250 w = 5.976 so, its perimeter is 2(w+7w) = 95.6
*October 2, 2015*

**Math**

(-2√2,0) Just graph the point. See that it is at the end of the diagonal of a square. Now rotate it.
*October 2, 2015*

**Geometry**

Check the related questions below. If they don't do the trick, come back with further details on why not.
*October 2, 2015*

**math**

10x = 32.222222... x = 3.2222222... subtract and you have 9x = 29 x = 29/9 Similarly, 4.(3) = 4 1/3 = 37/9 So, (29/9):(37/9) = 29:37
*October 2, 2015*

**math help**

"dash"?? Oh, please. Surely you can write y-axis! However, your answer is correct. Or, would be had you written (-5,3).
*October 2, 2015*

**science**

relative to what?
*October 2, 2015*

**Math OMG Please help**

clearly, the height at x=0 is 45. So, y = 45 - (3/31)x The x-intercept, naturally, is how far away from the platform the ramp's height is zero.
*October 2, 2015*

**Alegbra PLEASE HELP**

all right! geez, wait for a respone before posting it all over again.
*October 2, 2015*

**Alegbra**

while A and C both produce the same value, A is clearly the best choice, since it shows (-7) multiplied 5 times.
*October 2, 2015*

**I need help maths jus so confused**

this has no algebraic solution. You need some kind of graphical solution. Take a look at the graph of x^x - 100 = 0 and you will see that x ≈ 3.6 http://www.wolframalpha.com/input/?i=x^x-100+for+3%3Cx%3C4 That is reasonable, since 3^3 = 27 4^4 = 256
*October 2, 2015*

**Alegbra**

so do I.
*October 2, 2015*

**Geometry**

not bad, except that you did not follow instructions: To the nearest whole number Oh, that and the fact that 2π * 7 * 45 = 1979.2 You apparently approximated π by 3.14
*October 2, 2015*

**Geometry**

Looks good, except the h=45, not 14
*October 2, 2015*

**Math/Algebra**

ummm, no. #1 (y√4)/(4*2) = (28√9)/(2*7) 2y/8 = 84/14 y = 84*4/14 = 24 #2 ok
*October 2, 2015*

**Math/Algebra**

y = kab/√c So, (y√c)/ab = k is constant. so, you want (y√4)/(4*2) = (28√9)/(2*7) Now just find y. y=kx/z^2 so, you want (y*25)/50 = (24*9)/27
*October 2, 2015*

**Math**

earth's circle is (x+4)^2 + (y+3)^2 = 60^2 So, the orbit is (x+4)^2 + (y+3)^2 = 60.4^2
*October 2, 2015*

**physics**

100Hz = 100cycles/s = 0.1cycle/ms 0.1cycle/ms * 80ms = 8 cycles
*October 2, 2015*

**math**

GCF(18,20) = 2. So, at most 2 groups can be made.
*October 2, 2015*

**MATH**

so, what is the shortest side? Then find its midpoint. Just use the distance formula, and recall that the midpoint's coordinates are the average of the endpoints' coordinates.
*October 2, 2015*

**Business Math**

#1 (679.99-599.99)/679.99 = 0.1176 or about 12% #2 (15-12)/12 = 25% #3 extra revenue during that week was 15*599.99 - 12*679.99 = 839.97 So, ...
*October 2, 2015*

**physics**

well, in t seconds it falls 4.9t^2 meters. Looks like t≈1
*October 2, 2015*

**Calculus 1**

well, just do it normally: y' = 1/(9x^2+7y^2) * (18x+14yy') Now just factor out the y' stuff. Or, rewrite as e^y = 9x^2 + 7y^2 e^y y' = 18x + 14yy' y' = 18x/(e^y-14y) = 18x/(9x^2+7y^2-14y)
*October 2, 2015*

**Calculus 1**

y(x) = (9lnx)/x y'(x) = 9(1-lnx)/x^2 y'(1) = 9 y'(e) = 0 Now just use the point-slope form of the lines.
*October 2, 2015*

**Foley**

angle 1 + angle 2 = 90° But I'm sure Maddie caught that...
*October 2, 2015*

**Math**

well, they all add up to 360, so ...
*October 2, 2015*

**math**

you have it exactly backwards. To find out how many times 2 divides 10, you divide 10/2, not 2/10. So, 16.3/0.1 = 163
*October 2, 2015*

**physics**

E is in kg-m^2/s^2 p is in kg/m^3 A is in m^2 g is in m/s^2 So, we have kg-m^2/s^2 = kg^2/m^6 m^2/s^4 m^2 C kg-m^2/s^2 = kg^2/m^2-s^4 C C = (kg-m^2/s^2)(m^2-s^4/kg^2) = m^2-s^2/kg
*October 2, 2015*

**Maths**

(x-√2)(x+√2) = x^2-2 (2x^4+7x^3-19x^2-14x+30)/(x^2-2) = 2x^2+7x-15 Now you can factor that to find the other two roots
*October 2, 2015*

**Find x and y and also log**

2^x+y = 6 3^x-y = 4 6-2^x = 3^x-4 2^x+3^x = 10 A graphical solution is probably the best bet here. a^2+b^2=7ab a^2+2ab+b^2 = 9ab (a+b)^2 = 9ab 2log(a+b) = log 9ab log(a+b) = log(9ab)/2 = log√9ab = log√9 + log√ab = log3 + log(ab)/2 = log3 + (loga+logb)/2
*October 2, 2015*

**Math**

Does (0.025 + 1/2x) occur twice? It's hard to tell. If it does, and multiplies as written, then you just have 1.7 x 10^-3 = (0.0015 - x)^2 0.0015 - x = ±0.041 and that you can handle.
*October 2, 2015*

**Maths**

f(x) = x^2+8x-6 if the roots are 1/2 as much, then they are the roots of f(2x) = 4x^2+16x-6 I'll let you check with the quadratic formula.
*October 2, 2015*

**College Algebra**

clearly you are intended to use the Rational Zeroes Theorem, and start guessing. A little synthetic division reveals that there are no rational roots at all. So, the only possible roots will involve cube roots, and be very hard to find. I suggest graphing it and approximating ...
*October 2, 2015*

**Spanish**

Hi Sra! Could you please check my answers on these questions? 1) -Como quiera. Mientras Ud. ______ un sobre, yo limpiaré el compartimento. (MIRAR / BUSCAR) - Busque 2) Pero, por favor, antes de que Ud. se ________, (IR / VER) - Vayas 3) Cuando llegues (8) _____, ven (9...
*October 1, 2015*

**Math**

if it's air speed is 267 ft/s, then its vertical speed is 267 sin 16° = 73.595 ft/s So, to gain an altitude of 12500 ft takes 12500/73.595 = 169.848 seconds, or 2.83 minutes
*October 1, 2015*

**algebra**

the fraction left after d days is 0.5^(d/140) So, after 1 day, that is 0.99506 for a daily decay rate of 0.494% Now just plug in d=425
*October 1, 2015*

**Pre-calculus**

correct.
*October 1, 2015*

**Maths**

since it's a cubic, it's hard to do without calculus. The easiest way is to examine its graph. http://www.wolframalpha.com/input/?i=0.2t%28t-5.1%29%28t-9.1%29 Looks like t≈2.1 or 7.4
*October 1, 2015*

**Sequences and Series**

ahem. what is 25-3*8? minus, not plus.
*October 1, 2015*

**please help!!**

Assuming you meant f = (2x-6)/(x+1) using the quotient rule, f' = [(2)(x+1)-(2x-6)(1)]/(x+1)^2 so, at x=0, f' = (2+6)/2 = 4 Or, you can note that f = (2x-6)/(x+1) = 2 - 8/(x+1) so, f' = 8/(x+1)^2 f'(0) = 8/2 = 4
*October 1, 2015*

**math**

clearly it is 4160/x
*October 1, 2015*

**Math - eh?**

Try proofreading your posts.
*October 1, 2015*

**astronomy**

1 Watt = 1 J/s = 10^7 erg/s 1GW = 10^9 J/s the area of the sun is 4pi*(7*10^5 km)^2 = 6.2*10^12 km^2 So the solar output is 4*10^17 GW/6.2*10^12km^2 = 6.452*10^4 GW/km^2 So, now the question is: how much of that reaches the earth? I guess you need to use the inverse-square law...
*October 1, 2015*

**astronomy**

1/2 " = 2.424*10^-6 radians So, find r using s = rθ
*October 1, 2015*

**math?**

Not A: The contrapositive of X is if you don't raise your heart rate, you did not run for 10 min.
*October 1, 2015*

**AP Calculus**

if the rectangle is x wide by y high, then the diameter of the window is x. So x + 2y + π/2 x = 72 thus, y = [72-(1 + π/2)x]/2 The area is a = xy + π/8 x^2 = x[72-(1 + π/2)x]/2 + π/8 x^2 = 36x - (1+π/4)x^2 + π/8 x^2 = 36x - (1 + 3π/8)x^2...
*October 1, 2015*

**Help!! Geometric progression**

r=2, so you want a(2^(2n)-1) = 33a(2^n-1) n=5 ar * ar^3 = 2ar^4 a(r^4-1)/(r-1) = 80 a=2, r=3 GP: 2,6,18,54,162
*October 1, 2015*

**Math**

the same. You have just divided by m^4/m^4 = 1
*October 1, 2015*

**Physics**

clearly not, since you know that sound travels at roughly 373 m/s. Better double-check your math. Watch your units.
*October 1, 2015*

**functions**

no idea what differentiation of GIF means, but the derivative of a constant is zero (since constants do not change!). And, yes dx/dx = 1.
*October 1, 2015*

**Perumutation**

pick one of the antagonists. There are 8*7 ways to pick the two women next to her. There are 6! ways to arrange the other 6 women. So, 8*7*6! = 8! ways to seat the group.
*October 1, 2015*

**math**

at least means >= (not less) at most means <= (not more) #3: 8500 <= x <= 12000 #4 between usually includes the end points. So 6 <= x <= 8 #5: same idea #8: Using simple interest, 5000(1+10r) >= 1500 1+10r >= 1.30 10r >= 0.3 r >= 0.03 so, at least 3%
*October 1, 2015*

**algebra - eh?**

Fix the typo(s) You cannot add 100% antifreeze to 40% antifreeze and wind up with 25% antifreeze. Either you are adding water, or you have 10% antifreeze.
*October 1, 2015*

**Math**

well, which is greater -- 875 or 780?
*October 1, 2015*

**mass volume ratio**

so clearly each mole of Zn produces 1 mole of H2 6.5g = 0.1 mole Zn So, since 1 mole of H2 occupies 22.4L at STP, ...
*October 1, 2015*

**Math**

velocity v = ds/dt dx/dt = 2cos(t) dy/dt = -3sin(t) dz/dt = 1 acceleration a = dv/dt x" = -2sin(t) y" = -3cos(t) z" = 0 jerk j = da/dt x"' = -2cos(t) y"' = 3sin(t) z"' = 0
*October 1, 2015*

**pre-algebra**

cool. pretty small, eh?
*October 1, 2015*

**math**

well, she clearly can make 14/7 = 2 candles per box of wax. That help?
*October 1, 2015*

**@Reiny - Spoiler Alert**

Dang it, buddy, you're taking all the mystery out of math!
*October 1, 2015*

**Sphere find x**

if the diameter scales by a factor of x, the volume grows by x^3. So, if d -> 1.2d v -> 1.2^3 v = 1.728v That is, it grows by 72.8%
*October 1, 2015*

**Math 71x**

I assume plan B is a flat $30/month. If so, the costs are equal for x minutes if 20+0.04(x-200) = 30 And the question is poorly worded.
*October 1, 2015*

**math**

no clue. If all you have are inputs, how do you expect to find a rule? I expect you have not posted the problem as it was asked.
*October 1, 2015*

**Math**

assuming that the area is divided into three 25x40 areas, then the fencing needed is 2*75 + 4*40 If you want three 75 x 40/3 areas, that's different.
*October 1, 2015*

**trigonometry**

Just in case that wasn't enough of a hint, draw your diagram and notice that streetwidth = 30 cot15° - 30cot50°
*September 30, 2015*

**trigonometry**

use the cot function.
*September 30, 2015*

**Science**

How do binomial or 2 part names compare with early versions of scientific names? shorter longer descriptive in English my answer is descriptive
*September 30, 2015*

**math**

ah- much better. We need 4/5 B + 4/5 = B 4/5 = 1/5 B B = 4 Check: On Box A's side, we have 4/5 * 4 + 4/5 = 16/5 + 4/5 = 20/5 = 4
*September 30, 2015*

**Math**

no idea. what does b have to do with a scale balanced by box a and a 4/5 lb weight?
*September 30, 2015*

**math**

what's with all these expanding polynomials? That gives no extra insight whatever g = 1/(x^2+1) g' = -2x/(x^2+1)^2 g" = 2(3x^2-1)/(x^2+1)^3 since x^2+1 is always positive, g" is negative where 3x^2-1 < 0 x^2 < 1/3 That is on the interval (-1/√3,1...
*September 30, 2015*

**Permutations**

clearly, that is 10! = 3628800 Although, if all you care about is win, place, show then there are only 10!/7! = 720 ways to finish in the first 3 places.
*September 30, 2015*

**Math**

consider the total points. The total so far is 326. If the last grade is x, then you need 350 <= 326+x < 400 24 <= x < 74 If the 5th test counts as two, then it's like having six scores: 420 <= 326+2x < 480 94 <= 2x < 154 47 <= x < 77
*September 30, 2015*

**Calculus**

so, do you have a problem taking the partials and showing that they fit the equation?
*September 30, 2015*

**Maths**

1.76 + 760/6 t = 760/5 t t = 0.69 So, A overtakes B in .069 minutes. How many meters did A travel?
*September 30, 2015*

**math for managers**

costs are equal after x miles if 38000 + 0.24x = 35600 + 0.30x Now you need to know how many miles/year he drives.
*September 30, 2015*

**Math**

Actually, since they give you volumes, you have no idea how many grams are in solution! A 40% solution of NaCl would have a lot less mass of solute than a 40% solution of Fe2O3!
*September 30, 2015*

**math**

well, what's 10*10^5 ?
*September 30, 2015*

**Multivariable calculus**

dy/dx = (dy/dt)/(dx/dt) = (1+cost) / (e^t)(t+1) Kind of a cool curve, with a little scaling added: http://www.wolframalpha.com/input/?i=parametric+plot+x%3Dt%2F100+e^%28t%2F100%29%2C+y%3Dt%2F100%2Bsint
*September 30, 2015*

**Math**

clearly, p(success) = 801/1789 just express that as a decimal.
*September 30, 2015*

**math fractions**

4.25mi/0.875hr * 4.5hr = 21.86 mi or, using fractions (17/4 mi)/(7/8 hr) * (9/2 hr) = 17/4 * 8/7 * 9/2 = 153/7 = 21 6/7 mi
*September 30, 2015*

**math**

If she gets x right, then she gets 80-x wrong. That means we need 2x - 1/2 (80-x) >= 100 5/2 x - 40 >= 100 5/2 x >= 140 x >= 56
*September 30, 2015*

**Maths**

s(0) = 0 a little calculus (or inspection of the graph) will show that the runner changed direction at t=2.1 and t=7.4 s=10 when t≈10 http://www.wolframalpha.com/input/?i=plot+y%3D0.2t%28t+-+5.1%29%28t+-+9.1%29%2C+y%3D10
*September 30, 2015*

**pre algebra**

blue:red = (2/3):(3/4) = 2/3 * 4/3 = 8/9 after all, 2/3 = 8/12 and 3/4 = 9/12
*September 30, 2015*

**Go with Reiny**

Oops. I misread the problem.
*September 30, 2015*