Saturday
November 29, 2014

Posts by STEVE


Total # Posts: 27,054

Homework (Science)
it hits the ground when the height is zero. So, just solve 32.5t - 4.9t^2 = 0
October 21, 2014

Math
consecutive integers differ by 1. Pick any two adjacent elements of the list below: 1,2,3,4,5,6,7,8,9,... For example, 6 and 7. Those are consecutive integers. SO, you have two numbers, a=n and b=n+1 n/2 + (n+1)/2 = (n + n+1)/2 = (2n+1)/2 = n + 1/2 Since n is positive, n >...
October 21, 2014

Algebra
Change the 60 to -60 and then the underlined portion will be correct. Changing the underlined 20 to -20 would also work, but then you have nonsense: -3 < N < -20 which cannot be true for any value of N If you know about tags, you can use the u and /u tags to enclose ...
October 21, 2014

math
229 is clearly bogus! That is below the mean! I get 1.75 std above the mean for the top 4% better check that figure again.
October 20, 2014

Pre-Calc
(T-A)/(To-A) = e^-kt We have (60-93)/(45-93) = e^(-23k) e^(-23k) = .6875 k = .0163 So, now we want to find when T=77 e^(-.0163t) = (77-93)/(45-93) = 0.333 t = 67.4 minutes Nice model, but I'm sure that in real life, after more than an hour, that pop is very nearly 93 degrees!
October 20, 2014

Math
10 ∑(2k+4) = 144 k=2 You want to find the upper summation limit for the other values. So, what is n ∑(2k+4) = n(n+5) k=1 Note that Sum(2,10) = sum(1,10) - sum(1,1) = 150-6 = 144 Sum(4,12) = Sum(1,12)-Sum(1,3) = 204-24 = 180
October 20, 2014

Math 11
(A) 19 cot25° + 26.8 cot47° (B) 19 csc25° + 26.8 csc47° Draw a diagram and review your basic trig function definitions
October 20, 2014

math
how many digits? You could have anything from 2 to 11111111...2 where there are 98 1's
October 20, 2014

calc
so, how many intervals? Give us your idea of a table of values for the approximation.
October 20, 2014

Physics
A car drives straight down toward the bottom of a valley and up the other side on a road whose bottom has a radius of curvature of 100m . At the very bottom, the normal force on the driver is twice his weight. At what speed was the car traveling?
October 20, 2014

calculus
f'(x) = 2x-5 f'(1) = -3 So, the line with slope -3 through (1,-2) is y+2 = -3(x-1) Not sure what your four-step process is.
October 20, 2014

Math
18 boys play something. If b play both, then 13+15-b = 18
October 20, 2014

Math
You want x such that x(1.029)^(9/12) = 3262.50 x = 3193.29
October 20, 2014

Math
If there were n questions, then .80n = 22 n = 22/0.8 = ? Oddly, the result is not an integer. Typo? Rounded score?
October 20, 2014

calculus
f(t) = 1/3 (9t^2 + t^5) f'(t) = 1/3 (18t + 5t^4) = 1/3 t(18+5t^4) f'=0 where x=0 or ±∜3.6
October 20, 2014

MATHS
Assuming a typo, I have 6m^2 + 31m + 33 = 0 (2m+3)(3m+11) = 0
October 20, 2014

Calculus
since e^4x is always positive, and f'(x) = 2x e^4x (2x+1) f'=0 when x=0 or x = -1/2 f' < 0 where x < -1/2 f' > 0 where -1/2 < x < 0 f' > 0 where x > 0 This is clearly shown at http://www.wolframalpha.com/input/?i=+x^2+e^%284x%29+for+-1...
October 20, 2014

Calculus
f(x) = 2x/(6x+12) f(1) = 1/9 f(4) = 2/9 (f(4)-f(1))/(4-1) = 1/27 The MVT says that there is c in [1,4] such that f'(c) = 1/135 f'(x) = 2/3 (x+2)^-2 So, 2/3 (c+2)^-2 = 1/27 c = 2.24 which is inside [1,4]
October 20, 2014

Math
just use the double-angle formula: cos2A = 2cos^2 A - 1
October 20, 2014

Math
what does "2x6x" mean
October 20, 2014

Algebra
hmmm taht would be when 110-30t = 40 so, just solve for t. Also, lose the "m".
October 19, 2014

Algebra
Start from 110 feet away, a person on a bicycle rides toward a checkpoint and then passes it. The rider is traveling at a constant of 30m feet per second. The distance between the bicycle and the checkpoint is given by the equation d=(110-30t). At what times is the bike 40 ...
October 19, 2014

physics
Treat the i and j components separately Also, noting that F = ma, (30.7-12.0+x) = -8.00*2.44 (17.0+8.00+y) = 6.00*2.44 That will give you the third force, xi+yj
October 19, 2014

Math/Science
Unless you tell us something about the velocity of the resulting 3-bullet lump, there's no way to tell anything about its mass. Also, are the three gun muzzles arranged in a circle parallel to the plane of the target?
October 19, 2014

Calculus
when the water has height y, its surface has diameter 4/6 y. So, v = 1/3 pi y^2 (2y/3) = 2/9 pi r^3 dv/dt = 2/3 pi r^2 dr/dt Now just plug in your numbers.
October 19, 2014

Calculus
Draw a diagram. If the boat is x meters from the pier, the rope haas length r, with r^2 = x^2+1 So, 2r dr/dt = 2x dx/dt when x=5, r=√26, so 2√26(-1) = 2(5) dx/dt dx/dt = -√26/5 so, the boat is approaching the dock at about 1.0 m/s Makes sense, since x and r ...
October 19, 2014

Math
No, (B). A occurs when the degree of deg(p) <= deg(q) C occurs where q(x) = 0 and p(x) ≠ 0 D occurs when deg(p) = deg(q)+1 where deg(p) is the degree of polynomial p(x) You were obviously grasping, since even your suggested answer did not match its description.
October 19, 2014

math
just google "pyramid area" and plug your numbers into the formula shown.
October 19, 2014

geometry
Y = ((5-1)/2,(5+5)/2) = (2,5) (-2,2) = ((X1+2)/2,(X2+8)/2) So, X = (-6,-4)
October 19, 2014

Calculus
the slope of the tangent line at x=a is 1/a. If the line goes through the origin, its equation is y = kx. Clearly, at x=e, the line through (e,1) has slope 1/e. So, a=e see http://www.wolframalpha.com/input/?i=plot+y%3Dlnx%2C+y+%3D+1%2Fe+x
October 19, 2014

math
each face is an isosceles triangle with base = 26 height = 35.4 I'm sure you know (a) how to find the area of a triangle (b) how many faces the pyramid has plug and chug
October 19, 2014

Calculus
y' = 4 * 2cos(x^3)(-sin(x^3))(3x^2) = 4(2)(cos 1)(-sin 1)(3) = -10.9 Looks like you got lost somewhere in the chain rule
October 19, 2014

algebra
since time = distance/speed, then if the first speed was x mph, 600/x = 600/(x+40) + 4 x = 60 Check: outbound: 60 mph: 10 hrs return: 100 mph: 6 hrs
October 19, 2014

Math
Assuming the ball's diameter is the smallest dimension of the block, it is 10cm in diameter. So, the fraction of the block occupied by the ball is (pi/6 * 10^3)/(14*12*10) = 31%
October 19, 2014

Trigonometry
draw a diagram. It is clear that tan 24° = (h-6)/70
October 19, 2014

Math
tanx = sinx/cosx, but (tanx)' = sec^2(x) 1 + .5(9/4) + 4 = 6.125
October 19, 2014

College Algebra 1
-4(x+9)^3(x-11)^4(x+6)>0 Since the (x-11)^4 is always positive for x≠11, and the -4 is always negative, and n^3 has the same sign as n, you really just have to worry about (x+9)(x+6) < 0 In between -6 and -9, x+9 > 0 and x+6 < 0, so the interval you need is...
October 19, 2014

college algebra
that said, here's a tip: 2x^2+x-21 = (2x+7)(x-3)
October 19, 2014

college algeba
First off, how about typing r(x) on one line? Is there a division in there somewhere? If so, do you mean r(x) = 6x/(x+8) ?? Whatever r(x) is, to evaluate at some value, just substitute that value in everywhere there's an x: r(2) = (6*2)/(2+8) = 12/10 Now just plug and chug...
October 19, 2014

college algebra
it drops 6000/year, so you will have -6000t in there somewhere. v started at 80000 That should do it.
October 19, 2014

Algebra
-6-2 = -8 5-(-3) = 8 ... so the subtrahend starts out with 2x^4-3x^3... Just look at the coefficients of like powers. They threw you a curve by scrambling up the order of the powers. The first step would be to write the polynomials in descending order, so it's easier to ...
October 19, 2014

calculus
If I read your formula correctly, f(x) = 12x cos(5x)-(30√3 x^2) + 16 The slope at any point on the curve is f'(x) = 12(cos5x - 5x(sin5x + √3)) So, the equation of the tangent line at x=h is y-f(h) = f'(h)(x-h) y-(12h cos(5h)-(30√3 h^2) + 16) = (12(...
October 19, 2014

Math
the new area is (1.1L)(0.9W) = 0.99 LW so now you can tell how much the area has changed.
October 19, 2014

Math
If there are g glasses of skim and m servings of meat .1g + 3.75m = 7.36 8.2g + 21m = 73 Now just solve and you get g = 4.16 m = 1.85
October 19, 2014

Algebra
Look for the low-hanging fruit first. No easy roots, like 1 or 2, but we do find F(x) = (x+4)(2x^3-13x^2+32x-13) =(x+4)(2x-1)(x^2-6x+13) Now use the quadratic formula for the complex roots. This one was a little messy, since the roots took a little trial and error. Synthetic ...
October 19, 2014

math
well, 5*4*3 = 60 so, r = 3
October 19, 2014

algebra
If |a+5| = 9, either a+5 = 9 or a+5 = -9 So, a = 4 or -14
October 19, 2014

algebra
f(x) = (2x+7)(x-3)
October 19, 2014

Math
you know the minimum value is midway between the roots, which are -4 and 2p. So, the vertex is at x = (-4+2p)/2 = p-2 So, now we want the y-coordinate of the vertex, which is y = 2(p-2+4)(p-2-2p) = 2(p+2)(-p-2) = -2(p+2)^2 If that is -18, then -2(p+2)^2 = -18 p+2 = ±3, ...
October 19, 2014

math
#2 x and y are related, but not directly or inversely. C and D are just nonsense. Weird question and answers. divide $780 into 4 parts of $195 each one part into savings, 3 parts into checking. So, $195 into savings $585 into savings
October 19, 2014

Calculus
f = (ln x)^x ln f = x ln(lnx) 1/f f' = ln(lnx) + x(1/lnx)*1/x f' = (lnx)^x * (ln(lnx) + 1/lnx) This agrees with the extension of the normal power/exponent rule. If y = u^v where u and v are functions of x, then y' = v u^(v-1) u' + lnu * u^v v' = u^v (v/u u...
October 19, 2014

Math
The principal property of 0 is that for any real a, a*0 = 0 Now, suppose that we want to divide by 0. That means that if a/0 = b, then a = b*0 But b*0 is 0 for any b. That is, there is no real value of b for which b*0 is a nonzero number a. Think of the quotient when the ...
October 19, 2014

AP Calc. AB
y = dV/dt = 100,000 * 2(1 - t/50)(-1/50) = -4000 (1 - t/50) = -4000 + 80t This is (e) with all the noise removed
October 18, 2014

calculus
Since the domain of log(x) is x > 0, we need log(x) > 0 that is, 0 < x < 0.2 You can see this reflected in the graph found below. The domain is where the imaginary part is zero. http://www.wolframalpha.com/input/?i=log_.2%28log_.2%28x%29%29
October 18, 2014

ALGEBRA
just plug in -c for all the w's. A(-c) = √((-c)^2+13) = √(c^2+13)
October 18, 2014

algebra
since f|9| = f|-9| = 9, either x+5 = 9 or x+5 = -9 That's easy, now, right?
October 18, 2014

calculus
if the diagonal is d and the area is a, then we have d^2 = 2s^2 a = s^2 = d^2/2 now forget all that square root stuff, and use implicit differentiation: da = d dd we have a = 50, so d = 10 da = 4.45 4.45 = 10 dd dd = 0.45 You made a mistake in the line dD=A^(-1/2) dA It should...
October 18, 2014

Math
If there are g glasses of skim and m servings of meat .1g + 3.75m = 7.36 8.2g + 21m = 73 Now just solve and you get g = 4.1 m = 1.8 So, 5 glasses of mile and 2 servings of meat will provide the desired amounts
October 18, 2014

Calculus
correct all the way!
October 18, 2014

Calculus
correct
October 18, 2014

Calculus
this is exponential growth, where the rate of change is proportional to the population. Naturally, limited food will cause the population to level out, or even die off. Rather than just hang around for an answer, think about the hints given above. They contain all you need. ...
October 18, 2014

Math Algebra
correct.
October 18, 2014

calculus
how to factor what? ds/dt at t=5 is just 6*5+5 = 35
October 18, 2014

calculus
ds/dt is the velocity. Assuming you meant s(t) = 3t^2 + 5t + 3 ds/dt = 6t + 5 so plug in t=5.
October 18, 2014

calculus
look at the graphs here: http://www.wolframalpha.com/input/?i=plot+y+%3D+4cos%282x%29%2C+y%3D4 Now you have to clarify what you mean by "outside" a line
October 18, 2014

Algebra
#1 yes #2 no #3 no #4 yes why? a relation from x to y is a function if no x value maps to more than one y value. That is if f(a) = c and f(b)= c then a=b. Geometrically, it means that no vertical line can intersect the graph in more than one place. try graphing your relations ...
October 18, 2014

calculus
since x^2+y^2 = 36 2x dx/dt + 2y dy/dt = 0 when x=3, y=√27, so we have (3)(1/2) + √27 dy/dt = 0 so now you know how y is changing Since tanθ = y/x, sec^2θ dθ/dt = 1/x dy/dt - y/x^2 dx/dt Now just plug in your numbers again to find dθ/dt Of ...
October 18, 2014

Trigonometry
draw a diagram (h-2)/35 = tan60°
October 17, 2014

Calculus
this is exponential growth, where the rate of change is proportional to the population. Naturally, limited food will cause the population to level out, or even die off.
October 17, 2014

Calculus
This site discusses the problem, as well as a trick shortcut: http://math.stackexchange.com/questions/129249/maximize-volume-of-box-in-ellipsoid google will provide other solutions as well.
October 17, 2014

Algebra
The ordered pairs (1,6), (2,36), (3,216), (4,1296), and (5,7776) represent a function. What is a rule that represents this function?
October 17, 2014

MATH HELP PLEASE
Nope. all irrationals are real. It's gotta be B. How can a number be rational and irrational (which means NOT rational)?
October 17, 2014

Math
Not quite. The first term is 2/3, so the sum is 242/3 = 80 2/3 The first 4 terms are shown, and the next is 54. Their sum is 80 2/3 On #2, neither is a GP
October 17, 2014

Math
32/(1 + 1/2) = 64/3 you are correct
October 17, 2014

MATH HELP PLEASE
√21 is not 4.582575695 It is 4.582575695.... and is not a rational number How many different ways do we have to say the answer is CCCCCCCC??????
October 17, 2014

MATH HELP PLEASE
NO! 36 = 6^2, so sqrt(36) = 6, a rational number. 4^2 = 16 and 5^2 = 25 so 21 has no rational square root. The answer is C
October 17, 2014

Math
well, R·S = [-24/25,7/25] [-7/25,/24/25] Clearly this is a rotation matrix, for θ such that cosθ = 24/5 sinθ = 7/25 with appropriate signs. I forget where the + and - are applied.
October 17, 2014

Algebra
The ordered pairs (1,1), (2,8), (3,27), (4,64) , and (5,125) represent a function. What is a rule that represents this function? My answer is y = x cubed
October 17, 2014

Precalculus
you have (sinx-(cosx-1))/(sinx+(cosx-1)) multiply top and bottom by (sinx-(cosx-1)) and you have (sinx-(cosx-1))^2/(sin^2x - (cosx-1)^2) (sin^2x - 2sinx(cosx-1) + (cosx-1)^2) --------------------------------------- (sin^2x - cos^2x + 2cosx - 1) (sin^2x - 2sinx*cosx + 2sinx + ...
October 17, 2014

Math
use l'Hospital's rule. The limit is the same as [1/(1+h)]/1 = 1
October 17, 2014

Math
P = Po e^kt P/Po = e^kt kt = ln(P/Po) t = 1/k ln(P/Po) Just remember that e^x and ln(x) are inverse functions, just as √ and ^2 are inverses * and / are inverses + and - are inverses
October 17, 2014

MATH HELP PLEASE
Is 6 a rational number? YES! So, D is NOT the answer! A and B are also rational numbers. They are terminating decimals, so they are rational. Since 21 is not a perfect square (it is between 16 and 25) its square root is not rational.
October 17, 2014

MATH HELP PLEASE
√21 D is exactly 6
October 17, 2014

trigonometry
as usual, draw a diagram. You can easily see that if the distance is x, 2000/x = cos 60°
October 17, 2014

Trigonometry
the radius to (2,5) is at an angle θ such that tanθ = 5/2 So cosθ = 2/√29 sinθ = 5/√29 R' is at an angle (θ+45), so x = √29 cos(θ+45) y = √29 sin(θ+45) x = √29 (cosθ cos45 - sinθ sin45) = √29...
October 17, 2014

algebra
let's see what they say: .25q + 1.00d = 34.75 q = 3+4d Now just plug in q and you have .25(3+4d) + d = 34.75 .75 + 2d = 34.75 d = 17 so, q = 3+4d = 71
October 17, 2014

Math
2x^4 + 8/x^4 = 2(x^4 + 4/x^4) = 2(x^4 - 4 + 4/x^4) + 8 = 2(x^2 - 2/x^2)^2 + 8 This has its minimum value of 8 when x^2 - 2/x^2 = 0 x^4 - 2 = 0 x = ±∜2 ----------------------------- If there is only one point of intersection with the line y=x+c, then consider the ...
October 17, 2014

Math
You know that the minimum value is midway between the roots, so it occurs at x = ((-4)+(2p))/2 = p-2 So, we know that 2(p-2+4)(p-2-2p) = 2(p+2)(-2-p) = -2(p+2)^2 = -18 So, p+2 = 3 or -3 So, p = 1 or -5 Check: 2(x+4)(x-2) has its minimum at x = -1 2(3)(-3) = -18 2(x+4)(x+10) ...
October 17, 2014

Math
both correct
October 17, 2014

6th grade
just start listing them. If the order is cats, dogs, pigs, then he could have 12 1 1 11 2 1 11 1 2 10 3 1 10 2 2 10 1 3 and so on. If you look, you may discover a pattern to keep from having to list all of them.
October 17, 2014

Math
Just mentioning the 45 degree angle should have satisfied the teacher, since its sin and cos are both √2/2 IMO
October 17, 2014

Calc
Actually, it's shift 9 down then stretch vertically by 6 a stretch and then a shift is y = 6g(x) - 9
October 17, 2014

Calc
Describe e y = 6(g(x) - 9) as the result of first applying a stretch or compression and then applying a shift to g. First a ____________, by a factor of 6 __________ and then a ____________ by ________ units
October 17, 2014

mathematics
(60cm)(45cm)(x cm) = (54 dm^3)* (1000cm^3/dm^3) x = 20cm
October 17, 2014

calculus
what's the problem? Just use the good old quotient rule.
October 17, 2014

CALCULUS
The cross-section is a trapezoid of area (1+3)/2 * 6 = 12 m^2 So, the volume is 12 * 12 = 144 m^3 with only 1 m of water, the cross-section of the water is a triangle of area 3/2 m^2, so its volume of water is 18 m^3 Thus the pool is 18/144 = 1/8 full At depth y of water, the ...
October 17, 2014

math
You sure there's no typo here? The solution is really a mess: http://www.wolframalpha.com/input/?i=solve+y%22+%3D+3%28y-1%29^2&a=*C.solve-_*SolveWord-
October 17, 2014

calculus
f is decreasing when f' is negative and similarly for increasing f is concave down when f" is negative and similarly for concave up f = 3 + 4xe^-5x f' = 4(1-5x)e^-5x f" = 20(5x-2)e^-5x Hint: e^-5x is never zero
October 17, 2014

calculus
not sure what is the difference between an and {an} Do you mean |an|?
October 17, 2014

calculus
review your 1st and 2nd derivative meanings f' = -6(1+sinx)cosx f" = 6(sinx-cos(2x))
October 17, 2014

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