Saturday

July 23, 2016
Total # Posts: 42,010

**calculus**

find the max of f(x) = x*p(x)-c(x) = x(300-x)-(20000+24x+1/2 x^2) = -3/2 x^2 + 276x - 20000 f' = -3x + 276 f'=0 at x=92 since f" < 0, that is a max.
*May 12, 2016*

**Pre Calculus**

there are many good calculators for this online.
*May 12, 2016*

**Math**

here are the graphs. Compare them. http://www.wolframalpha.com/input/?i=plot+y+%3D+-0.7%2Fx,+y%3D-0.9%2Fx
*May 12, 2016*

**math**

c = 2πr a = πr^2 so, plug in various values for r: r c a 1 2π π 2 4π 4π ... 16 32π 256π when 2r is substituted for r, you have new values for c and a: 2π(2r) and π(2r)^2 compare those to the original values using just r.
*May 12, 2016*

**Functions**

correct
*May 12, 2016*

**Functions**

clearly, R3 = R1+R2
*May 12, 2016*

**Functions**

15% loss means each year the value is 0.85 what it was.
*May 12, 2016*

**math**

a point (x,y) on the ellipse is (x,(1/5)√(225-9x^2)) halfway there is (x/2,(1/10)√(225-9x^2)) x^2/4 + y^2/b^2 = 1 x^2/4 + (225-9x^2)/100b^2 = 1 25b^2x^2/4 + 225-9x^2 = 100b^2 (25b^2/4 - 9)x^2 = 100b^2-225 25b^2/4 = =9 b^2 = 36/25 x^2/4 + (25/36)y^2 = 1 9x^2 + 25y^2...
*May 12, 2016*

**calculus 1**

as before, but with washers v = ∫[0,2] π(R^2-r^2) dx where R=6 and r=y+2=.25x^4+2
*May 11, 2016*

**calculus**

inverse trig functions are nasty, so we will try to use dx in both cases. around the x-axis use discs (washers) of thickness dx, v = ∫[0,2π] πr^2 dx where r = 3+sinx v = ∫[0,2π] π(3+sinx)^2 dx around the y-axis, use shells of thickness dx v = &#...
*May 11, 2016*

**Math**

since 40=2^3*5, the other number must be 2^3=8 no other primes or higher powers of 2 and 5 works.
*May 11, 2016*

**Math**

42
*May 11, 2016*

**math**

28/9 = ...
*May 11, 2016*

**math**

since distance = speed * time, 4(s+5) = 6(s-5)
*May 11, 2016*

**calc**

think of the volume as a lot of thin cylinders of thickness dx. v = ∫[0,2] 2πrh dx where r = x and h = 3-y = 4-x^2 v = ∫[0,2] 2πx(4-x^2) dx or, you can think of the volume as a stack of thin discs of thickness dy. Then v = ∫[-1,3] πr^2 dy where...
*May 11, 2016*

**Math**

just adjust the scale by a factor of 12: 1:228
*May 11, 2016*

**Math/Precal**

5C0(-4x)^5(-3)^0 + 5C1(-4x)^2(-3)^1 + 5C2(-4x)^3(-3)^2 = -1024x^5 -3840x^4 - 5760x^3
*May 11, 2016*

**Maths**

the angles add to 180, so the largest angle is 95 now use the law of sines to find x, the shortest side: x/sin37 = 267/sin95
*May 11, 2016*

**Math**

((9y-3)-(3y-7))/2 = 3y+2
*May 11, 2016*

**Math**

you are correct; the discriminant is positive.
*May 11, 2016*

**Math**

well, what is 1qt:1gal ? same ratio, right?
*May 11, 2016*

**Differential Calculus**

did you actually draw an isosceles triangle with a base of 10? A = 1/2 bh Let's not forget the basics now that we're in calculus!
*May 11, 2016*

**Differential Calculus**

we have the height h is h = 5tanθ a = 5h = 25tanθ da/dt = 25sec^2θ dθ/dt Now just plug in your numbers (in radians!)
*May 11, 2016*

**Calculus**

we have tanθ = h/4 sec^2θ dθ/dt = 1/4 dh/dt Now just plug in your numbers.
*May 11, 2016*

**Maths**

of course, this is a stupid question, since the tank and the jug are in gallons, who cares how many liters it is? 1 gallon = 231 in^3
*May 11, 2016*

**Maths**

rather than convert each dimension, let's just convert in^3 to cm^3 at the end: 11.8*19.7*15.7 * 2.54^3 cm^3 Note that he holy has to fill 1/2 the tank. Now you know how many liters, just convert that to gallons to find how many trips it will take.
*May 11, 2016*

**Calculus**

if the beam touches the ground x feet from the wall, and touches the building at a height of y feet, then x/3.375 = (x+8)/y y = (27/8)(x+8)/x The length z of the beam is z^2 = x^2+y^2 = x^2 + ((27/8)(x+8)/x)^2 Crank through the algebra, and you find that dz/dx=0 at x≈5....
*May 11, 2016*

**Calculus**

because that's the definition of tan(a): opposite/adjacent. Did you draw a diagram of the setup? That's the first step to all of these problems.
*May 11, 2016*

**Calculus**

If the angles to the bottom and top are a and b, then from a distance x we have tan(a) = 8/x tan(b) = 18/x We want the angle c=b-a, so c = arctan(18/x)-arctan(8/x) dc/dx = 10(144-x^2)/((x^2+8^2)(x^2+18^2)) dc/dx=0 at x=12
*May 11, 2016*

**MATH**

what, given the numbers, you can't write an expression that adds them up? Fie on thee!
*May 11, 2016*

**math**

you know that sin(x) has period 2pi. So, since x/2 changes half as fast, it has period 4pi: y = 2sin(x/2)
*May 11, 2016*

**Algebra**

You have mangled your expressions. I cannot parse them at all. I suggest you go to wolframalpha.com and type in your expressions. Watch to see how they get interpreted, and use parentheses till you get what you expect.
*May 11, 2016*

**Pre algebra**

clearly B is wrong, since 1/3 (-3) - 8 = -1-8 = -9 Note that y changes by -3 when x changes by 1. So, the slope is -3. So, check A and D to see which works.
*May 11, 2016*

**Math**

x^3 is the 4th term. So 5C4 2^2 x^3 = 10*4*x^3 = 40x^3
*May 11, 2016*

**7th Math**

of the 36 possible outcomes, only one is 6,6
*May 11, 2016*

**MATHS**

on each draw, the probability is easy to get. Just multiply them together, as the draws are independent events.
*May 11, 2016*

**MATH**

2/7 * 5/7
*May 11, 2016*

**math**

j=4d j+4 = 3(d+4) now just solve for j and d.
*May 11, 2016*

**Math**

amateur
*May 11, 2016*

**Math **

B looks good to me although technically there is a factor of 100 missing in there, since the answer is really 35%, not 35.
*May 11, 2016*

**MATH**

again? Just add up how many even outcomes there are, and divide by the number of spins. Same problem as before, just different numbers.
*May 11, 2016*

**Math **

right again.
*May 11, 2016*

**Math**

The major axis has length 12, and the center is midway between the two points given, or (1,2) (x-1)^2/16 + (y-2)^2/36 = 1
*May 11, 2016*

**math**

clearly, 102/300
*May 11, 2016*

**Math **

correct
*May 11, 2016*

**Simple Question**

military pay is generally rather low, at least in the beginning.
*May 11, 2016*

**math**

(a) h/126 = tan46° (b) (i) 72/x = tan46° (ii) 72/z = sin46°
*May 11, 2016*

**math**

just use the definition of n! 4! = 4*3*2*1
*May 11, 2016*

**Math**

you don't say which two lines, but I infer that they are x = -1 and x=1. The region is symmetric about the y-axis, so we can just double the area from 0 to 1. using discs, v = 2∫[0,1] π(R^2-r^2) dx where R=e^x and r=e^-x v = 2∫[0,1] π(e^2x - e^-2x) dx...
*May 11, 2016*

**Math**

well, what are 4-3 -2-0 -1-2 ??
*May 11, 2016*

**network programing**

adobe brick? cowhide? more likely lead paint or asbestos But not sure what that has to do with network programming...
*May 11, 2016*

**math**

well, looking at the graphs, it looks like -2 <= x <= 2 checking, if we call them f(x)+g(x) >= h(x), then f(-2) = 20√5 g(-2) = 0 f(2) = 0 g(2) = 20 h(-2) = 28 h(2) = 20 so, f(-2)+g(-2) >= h(-2) f(2) + g(2) >= h(2) Clearly we need x >= -2 for √(x+2...
*May 11, 2016*

**Calculus**

As Reiny says, a rectangle whose base goes from 0 to x has area a = xy = xe^(-x^2) da/dx = (1-2x^2) e^(-x^2) so there is a max at x = 1/√2 That is assuming, of course that the rectangle has its base on the x-axis. It might be possible that a rotated rectangle could be ...
*May 11, 2016*

**Math**

each roll gives 10 possible outcomes, so there are 10^4 events. I ain't gonna list them, but the list starts and ends with 1 1 1 1 1 1 1 1 ... 10 10 10 9 10 10 10 10
*May 11, 2016*

**maths**

well, every second the velocity increases by 0.2 m/s. So how much is that after 10 seconds?
*May 11, 2016*

**Algebra**

no, that is 6.08 x 10^-7 power Move the decimal point to the right for positive powers (multiplying by 10)
*May 11, 2016*

**math**

the diagonal is 90√2=127.28 feet, so the mound is not in the center of the diamond (63.64 ft from home). So, you can't use the Pythagorean Theorem here. Instead, use the law of cosines: x^2 = 60.5^2 + 90^2 - 2*60.5*90*cos45° x = 63.72 feet
*May 11, 2016*

**math**

just use what you know about geometric sequences: S14 = 25(1.1^14-1)/(1.14-1) = 499.55 km
*May 10, 2016*

**Math**

your answer is good, but there are other systems with 3 sets of axes which do the same job. try googling your question. You will see discussions of the other characteristics of the system.
*May 10, 2016*

**Math**

since 1 qt is 1/4 of a gallon, you can go 1/4 as far: 9mi/qt or, using the proper units, get the gallons to cancel: 36 mi/gal * 1gal/4qt = 36/4 mi/qt
*May 10, 2016*

**Math**

18^2 + h^2 = 82^2
*May 10, 2016*

**math: permutations**

correct.
*May 10, 2016*

**Math help ASAP please**

well, plug in t=7. -16*49 + 96*7 = -112 You must be guessing, not calculating. When the ball hits the ground, its height is zero, right? Note that h(t) = -16t(t-6) Now, when is h=0?
*May 10, 2016*

**Math **

come on. You want to land in one of 10 equal areas. The chance is 1/2? Try again.
*May 10, 2016*

**Math**

well, 54+36 = 90
*May 10, 2016*

**math**

Also, sometimes someone comes in and just dumps a lot of homework questions with no indication they plan to do any work on their own. And some questions are so garbled or silly they cannot be deciphered, or do not deserve an answer.
*May 10, 2016*

**math**

usually because no one among the tutors has the particular expertise needed at the time.
*May 10, 2016*

**maths**

because sin(x) is positive in that domain. Your answer is incomplete because you only mentioned QII.
*May 10, 2016*

**Algebra**

so, now it's down to A or D. Do the math...
*May 10, 2016*

**Algebra**

you have 5(2x^3+6x-4) / -5(x-5) = -(2x^3+6x-4)/(x-5) a little synthetic division shows that it does not divide evenly. I suspect a typo. However, it is clear that only B or C could work, even after the typos is fixed.
*May 10, 2016*

**Geometry**

Let M be the midpoint of AD. Then you have two right triangles BMA and DMC where you know the hypotenuse and one leg. Use the Pythagorean Theorem to find BM and MC.
*May 10, 2016*

**Nutz**

–0.5(4 + x) = –1.3 -2.0 - 0.5x = -1.3 -0.5x = 0.7 ...
*May 10, 2016*

**math**

man - have you ever seen the graphs? google is your friend, as is your textbook. both are conic sections, but a parabola has eccentricity = 1 an ellipse has eccentricity < 1
*May 10, 2016*

**MATH HELP PLEASE**

#1 nope. you missed a minus sign #2 could be right, if there was supposed to be a +5 in there #3 nope #4 nope #5 nope. you added, but you should have subtracted. If I ask how much bigger 6 is than 2, you don't add 6+2. #6 nope. you add exponents when multiplying powers. ...
*May 10, 2016*

**Algebra**

collect like terms and you get 8x^2+8x-3
*May 10, 2016*

**Math Please Help**

#1 ok #2 nope. You picked the chance of getting a vowel, but that's not what they asked. #3 ok #4 ok #5 ok
*May 10, 2016*

**Analytic Geometry**

you know it has a double root at x=0 so, the graph is tangent to the x-axis at (0,0) The graph crosses the x-axis at x=4 y is positive for large negative values of x, so the graph comes down from the left, touches (0,0), goes back up and crosses at (4,0) on its way down to the...
*May 10, 2016*

**calculus**

Hmmm. I misspoke. The average value is ∫[0,2] V(t) dt -------------------- 2-0 = 0.3010
*May 10, 2016*

**calculus**

That would just be (V(2)-V(0))/(2-0) = 0.6554/2 = 0.3277
*May 10, 2016*

**Linear Algebra - urgent!**

google is your friend. You could start here: http://math.stackexchange.com/questions/986859/why-is-deta-lambda-i-lambda-cn-when-a-cin-0
*May 10, 2016*

**Algebra 2**

not quite sure what you mean by t time is on 120 sec From what you said, it appears that h = at^2 + 35000 But, from the two data given, it looks like h(120) = 35000
*May 10, 2016*

**Math**

well, jeez - look at the 7 row. How many 8's are there?
*May 10, 2016*

**Maths grade 12**

of course , if siny = 0, then we have cosy = 1 or -1. You can try those for other solutions.
*May 10, 2016*

**Math (please help)**

the box is 8" long, so the paper has to be long enough to wrap around the ends. I'd say (D)
*May 10, 2016*

**math**

center is at (-6,5) so (x+6)^2/a^2 + (y-5)^2/b^2 = 1 The semi-major axis is vertical,and of length 13. c^2 = a^2-b^2 165 = 169-4, so b=2 (x+6)^2/4 + (y-5)^2/169 = 1 see http://www.wolframalpha.com/input/?i=ellipse+%28x%2B6%29^2%2F4+%2B+%28y-5%29^2%2F169+%3D+1
*May 10, 2016*

**maths**

recall that the product of the roots will be f/1 If f is prime, then the only possible rational roots will be ±1, ±f Since f and -f cannot both be roots (why?) there can be at most 3 rational roots. Furthermore, since f is positive (why?), -1 cannot be a root, ...
*May 10, 2016*

**calculus sir damon help me or steve**

recall your half-angle formulas for hyperbolic functions: sinh(x/2) = √((coshx-1)/2) so, √(coshx-1) = √2sinh(x/2) dx/√(coshx-1) = 1/√2 csch(x/2) dx now just use your standard form for integrating csch(u)
*May 10, 2016*

**math**

k = .6l l = .6m m-140 = l now just find k+l+m
*May 10, 2016*

**math**

a+b=108 3a/4 + (2/5)(b+a/4) = (3/5)(b+a/4) now just solve for b.
*May 10, 2016*

**geometry and trig**

If the cylinders are similar, then the ratio of volumes is (10/4)^3 as much, or 15.625 lbs = 250 oz how did you get 137pi? I suspect something is left unsaid here, as none of the choices seems right.
*May 10, 2016*

**algebra 1**

well, he is 1.75 std above the mean, or 28 + 1.75 * 8
*May 10, 2016*

**Mayh**

1/2 of 1/2 = 1/4
*May 10, 2016*

**math: probability**

wrong.
*May 10, 2016*

**math: probability**

correct, if you replace the first card before drawing the second.
*May 9, 2016*

**Algebra**

ignoring the mysterious comma, 3fg(f^2+5f-4) = 3f^3g + 15f^2g - 12fg
*May 9, 2016*

**math**

sounds like a rectangle to me.
*May 9, 2016*

**Science**

the same
*May 9, 2016*

**calculus**

(lnx)/(x) x^(lnx-1) = x^(lnx)/x
*May 9, 2016*

**calculus**

Is the lnx/x suppose to be (lnx)/(x) or ln(x/x)?
*May 9, 2016*

**calculus**

I don't understand how you went from y' = lnx x^(lnx -1) + lnx x^lnx (1/x) to lnx/x x^lnx + lnx/x x^lnx. Where did the -1 go? May you please explain?
*May 9, 2016*