Thursday
May 5, 2016

Posts by Steve

Total # Posts: 40,202

math plz its urgent
I also think B is correct. Starts at -4 and keeps going down by 2 each step.
March 16, 2016

Statistic
play around with Z table stuff at http://davidmlane.com/hyperstat/z_table.html and you can see how it works.
March 16, 2016

geometry
thank you
March 16, 2016

geometry
I agree.
March 16, 2016

geometry
Find the missing value to the nearest hundredth. tan ___ = 73 a- 81.61 b- 64.61 c- 60.61 d- 89.22 My answer is D
March 16, 2016

math
volume of earth is π*(3/2)^2 * 14 = 63π/2 m^3 The area of the ring is π(4 + 3/2)^2 - (3/2)^2) = 28π m^2 So, the thickness of the ring is (63π/2 m^3) ÷ (28π m^2) = 9/8 m
March 16, 2016

Math
just be counting things when she's around. (No, not all the time, just when it seems like an opportune moment.) When she's ready, she'll take an interest, and then watch out; there'll be no stopping her. I don't know how many sheets of paper I used up as a ...
March 16, 2016

Math
subtract 2 1/2 from both sides. That gives you b = 3 1/4 - 2 1/2 now simplify: b = 3/4
March 16, 2016

Math/Precal
sinx/(1-cosx) = sinx(1+cosx) / (1-cosx)(1+cosx) = sinx(1+cosx) / (1-cos^2x) = sinx(1+cosx) / sin^2x = (1+cosx)/sinx
March 16, 2016

maths
If the perimeters differ by 32, the sides differ by 8. s^2 + (s+8)^2 = 610 Now just find s and s+8.
March 16, 2016

maths
Of course, 1+2+3 does equal 1*2*3
March 16, 2016

Math/precal
not a joke. Just checking your knowledge of common identities and angles. So, the exact value is 0/1 = 0.
March 16, 2016

GEOMETRY/ALGEBRA
So, only B appears correct. C would work, if you consider 0.1 min/cm^3 a rate. Usually rates are written with time in the denominator. If, however, you want to determine the time needed to fill 1 cm^3, then C will work.
March 16, 2016

math
If the domain is {-3,0,1,5} then A
March 16, 2016

maths
You have some matching problems with braces and parens, but 2(fg)(2) = 2*f(2)*g(2) = 2*3*2 = 12 (f/g-2f)(3) = f(3)/g(3) - 2f(3) = 6/1 - 2*6 = -6 (f-g)(4) = f(4)-g(4) = 9-2/3 = 8 1/3 kobe needs to step back and take a breath.
March 16, 2016

calculus help!!!!! plz
As written, you have ∫cosx + 2/cosx + sinx dx which is just trivial: sinx + 2ln(secx+tanx) - cosx + C So, I'll assume you meant ∫(cosx + 2)/(cosx + sinx) dx That's tougher than it looks. cosx/(cosx+sinx) = 2cosx/2(cosx+sinx) = (cosx+sinx + cosx-sinx)/2(cosx...
March 16, 2016

Maths\relation&function
the domain of f+g is D(f) ∩ D(g) = {1,2} For other values, both f and g are not defined, so f+g cannot be defined. f+g = {(1,2+5),(2,5+5)} = {(1,7),(2,10)} do f-g the same way.
March 16, 2016

sequence help!!!!! plz steve,reiny,damon,bob...anyone!!!!
I suspect a typo. 6 = 1^3+5 13 = 2^3+5 32 = 3^3+5 69 = 4^3+5 130 = 5^3+5 221 = 6^3+5 If no typos, then I'm stuck, too.
March 16, 2016

Calculus
I'm intrigued how you got all those odd values for the areas when the width of each rectangle is 2 ....
March 15, 2016

Calculus
draw a diagram. At time t hours, the distance z is z^2 = (20t)^2 + (25t)^2 now just figure dz/dt at t=2.
March 15, 2016

Math
well, the sides are 4, 4√3 and 8
March 15, 2016

math
such a reflection moves (x,y) -> (-x,y)
March 15, 2016

Math
beats me. I don't see any variables at all. usually the independent values are listed first.
March 15, 2016

math
use a common denominator of 21
March 15, 2016

Algebra
x+y=38 y=x+8
March 15, 2016

math
h/50 = sin54°
March 15, 2016

Math
correct
March 15, 2016

math
If the tank is on end, then if the depth is d ft, the volume is π*3^2*d = 9πd ft^3 So, if 2 ft deep, that's 18π=56.5 ft^3 However, if the tank is lying on its side, so the axis is horizontal, then we have to figure the area of a circular segment - the cross-...
March 15, 2016

Math
correct, but the ratio also increases. The volume grows faster than the area. Consider a cube of side s. v = s^3 a = 6s^2 v/a = s/6 So, the actual ratio depends on the size of the cube. No matter what the shape, the ratio of volume to area gets larger and larger as the size ...
March 15, 2016

Math
the triangle has three equal sides, then it is equilateral, so each of its angles is 60° The square's angles are all 90°. So, starting at the bottom of the triangle, and moving around, the angles are 60, 60+90=150, 90, 90, 150 Note that as with any pentagon, the ...
March 15, 2016

Geometry
No explanation needed, if you recall that the sum of the interior angles of a polygon with s sides is 180(s-2). So, 180(s-2) = 2880
March 15, 2016

math
The nth term is n. The sum of n terms is n(n+1)/2
March 15, 2016

Trig identity.
sin4x = 4sinxcos - 8sin^3x cosx sin4x = 4sinx*cosx(1-2sin^2x) sin4x = 4sinx*cosx(cos2x) sin4x = 2(2sinx*cosx)(cos2x) sin4x = 2(sin2x)(cos2x) sin4x = sin(2*2x) sin4x = sin4x cos3x cos(x+2x) cosx*cos2x - sinx*sin2x cosx(1-2sin^2x) - sinx(2sinx*cosx) cosx(1 - 2sin^2x - 2sin^2x) ...
March 15, 2016

Trig help
#1 must be a joke. sin2x=sin2x for all x #2 tan2x + tanx = 0 2tanx/(1-tan^2(x)) + tanx = 0 2tanx + tanx(1-tan^2(x)) = 0 tanx (2 + 1-tan^2x) = 0 tanx=0 tanx = ±√3 so, x=kπ or kπ ± π/3 Now just use the values of k so that the results come out ...
March 15, 2016

math
3 1/4 * 10 = 30 10/4 = 32 1/2
March 15, 2016

math -oops
My bad. opens to the left: x = ay^2 -1 = a*2^2 a = -1/4 x = -1/4 y^2 or y^2 = -4x http://www.wolframalpha.com/input/?i=y^2+%3D+-4x
March 15, 2016

math
vertex at (0,0) means y = ax^2 So, plug in (-1,2) and you have 2 = a(-1)^2 a = 2 so, y = 2x^2
March 15, 2016

Calculus
Hmmm. Let's trudge through those words. We have ∫[2,8] g(x) dx = 5 ∫[6,8] g(x) dx = -3 we know that ∫[2,6] + ∫[6,8] = ∫[2,8] ∫[2,6] + (-3) = 5 ∫[2,6] g(x) = 8 ∫[2,6] 2g(x) = 2*8 = 16 Forgot that 2, eh?
March 15, 2016

Calculus
Nope. ∫ 1/(x^2+1) dx :: not so simple here. You need x = tanθ The 2nd is the same, unless there are some groupings you have omitted. ∫ x/(x^2+1) dx :: u = x^2+1 ∫ x^3/(x^4+1) dx :: u = x^4+1
March 15, 2016

Calculus
nope. sums and differences work that way, but not products. Consider f(x) = x g(x) = x ∫f * ∫g = 1/2 x^2 * 1/2 x^2 = 1/4 x^4 ∫fg = ∫x^2 = 1/3 x^3 ∫f-g = ∫f - ∫g TRUE ∫[a,a] f(x) dx = 0 NOT 2∫[0,a] ∫3+f = ∫3 + &#...
March 15, 2016

Calculus
∫[0,2] e^(4x) dx = 1/4 e^(4x) + C [0,2] = (1/4 e^8 + C)-(1/4 e^0 + C) = 1/4 (e^8 - 1) remember that e^0=1, not 0.
March 15, 2016

Calculus
I assume that ‡ means ∞ You know that ln(x) is only defined for x in (0,∞) Your answer holds for f(x) = ln(|x|), not ln(x)
March 15, 2016

Calc
∫[2,5] 2+√x dx Looks like the last one to me. The three intervals are [2,3],[3,4],[4,5] The right endpoints are at 3,4,5, NOT 0,1,2,3
March 15, 2016

Geometry
true
March 15, 2016

maths
the lengths are in the ratio √(25/9) = 5/3
March 15, 2016

Calculus
x^2 y + ax - 2/5 (10+2a) y = 0 2xy + x^2y' + a - 2/5 (10+2a)y' = 0 y'(x^2-2/5 (10+2a)) = -(2xy+a) y' = 5(a+2xy)/(4(a+5)-5x^2) y" = 5(2y + 2xy')(4(a+5)-5x^2) - 5(a+2xy)(-10x) ----------------------------- (4(a+5)-5x^2)^2 5(2y + 2x(5(a+2xy)/(4(a+5)-5x^2...
March 15, 2016

Calculus
first off, if (2,2.5) is an inflection point, then it is on the graph. That means x^2 y + ax + by = 0 4*2.5 + 2a + 2.5b = 0 10 + 2a + 2.5b = 0 5/2 b = -(10+2a) b = -2/5 (10+2a) That gives us x^2 y + ax - 2/5 (10+2a) y = 0 y = -ax/(x^2 - 2/5 (10+2a)) = 5ax/(4(a+5)-5x^2) y'...
March 15, 2016

Pre-Calc
If it passes through (-2,16) and (-2,0) and (-32,0) then by symmetry the center must be at (-17,8) Now we can use any of the points to find that r = 17 so (x+17)^2 + (y-8)^2 = 17^2 see http://www.wolframalpha.com/input/?i=plot+%28x%2B17%29^2+%2B+%28y-8%29^2+%3D+17^2,+x%3D-2,y%...
March 15, 2016

precalc
well, geez, just factor out the e^(-2x): e^(-2x) (5x^2-3x^3) = 0 e^(-2x) x^2 (5-3x) = 0 That help?
March 15, 2016

precalc
2^(-x) (2^(2x) + 2*2^x - 8) = 0 2^(-x) is never zero, so that means you must have 2^(2x) + 2*2^x - 8 = 0 (2^x+4)(2^x-2) 2^x is never negative, so that means 2^x-2=0 2^x=2 x=1
March 15, 2016

Algebra 2
I'd say just solve for n. But looking here http://www.wolframalpha.com/input/?i=n^2%3D%281%2F2n%2B10%29%281%2F2n-2%29 it appears there is no solution. A typo in the problem?
March 15, 2016

Math
y = 6(1.21)^t 1.21 = e^ln(1.21) = e^0.19 y = 6*(e^0.19)^t = 6*e^(0.19t) Now you can work the rest
March 15, 2016

Calculus
you might start by reading up on Euler's method. google can help. There's even a youtube video illustrating the method. There's a good discussion with examples here: http://tutorial.math.lamar.edu/Classes/DE/EulersMethod.aspx
March 15, 2016

math
use 1/4 of 3c water and 1c cereal So, that's 1/4 c cereal.
March 14, 2016

Math
.75x = 30 x = 40 or, using fractions, 3/4 x = 30 3x = 120 x = 40
March 14, 2016

Pre-Calc
Grrrr! pi, not pie!!! Pie is what you eat. Other than that, why not use real math symbols, instead of all those messy words?? tan θ = -√22/11 and π/2 < π < π Draw the triangle in standard position. tanθ = y/x = √22/-11 sinθ = y/r...
March 14, 2016

calculus
see related questions below. And http://math.stackexchange.com/questions/225718/find-the-volume-of-the-largest-right-circular-cone-that-can-be-inscribed-in-a-sp
March 14, 2016

calculus
it is clear that h = 2r, so v = 1/3 πr^2 h = π/12 h^3 dv/dt = π/12 h^2 dh/dt so, now just crank it out: π/12 * 8^2 dh/dt = 8 dh/dt = 3/(2π) m/min
March 14, 2016

calc
xy=50, so y=50/x a = (x+4)(y+8) = (x+4)(50/x + 8) a = 8x + 200/x + 82 da/dx = 8 - 200/x^2 da/dx=0 if x=5 so, the inside dimensions are 5x10 and the outside is 9x18
March 14, 2016

calculus
a = 4πr^2 at t=2, a=52, so r=√(13/π) da/dt = 8πr dr/dt so, you need 8π√(13/π) dr/dt = 26 dr/dt = 1/4 √(13/π)
March 14, 2016

Math (geometry)
the whole circumference is 7926π. half the way around is 3963π. since the plane goes 550 miles each hour, it will take 3963π/550 = 22.6 hours
March 14, 2016

Geometry
You are correct. Draw a diagram, and if the belt's length is x, then 12/x = sin60°
March 14, 2016

math
35 * 6/7 * 4/5 = 24
March 14, 2016

Algebra
Your answer is right, but you should have typed the problem correctly.
March 14, 2016

Algebra
since every term has a "c" in it, 2c is the GCF, not just 2.
March 14, 2016

math
I'll write it, and then it'll be right. (2.74+5.6)x10^7 = 8.34x10^7
March 14, 2016

Alegbra
all multiples of 3-4-5 5-12-13 7-24-25 and other common sizes. I expect you can google the topic of pythagorean triples and find a suitable list.
March 14, 2016

Trigonometric Identities
tan(A+B) = (tanA+tanB)/(1-tanAtanB) that should get you started.
March 14, 2016

Trigonometric Identities
tanA-sinA = sin(1/cos - 1) see where that takes you.
March 14, 2016

math
I don't have the choices, but I suspect (0,4) was one of them. Then you'd have a 3-4-5 right triangle. If that's not one of them, then you'll have to check dot products. If one of the dot products is zero, then those two vectors are orthogonal.
March 14, 2016

Happy Pi Day, 2016
I find it transcendental.
March 14, 2016

Calculus
after the integration, you have arctan(1) - arctan(a) = arctan(1/a) - arctan(1) π/4 - arctan(a) = arctan(1/a) - π/4 rearrange the terms and you're done.
March 14, 2016

Math
area of triangle times the length.
March 14, 2016

Math
holy crap! Ever hear of math sumbols? 3/7, 2/3, 2/5 Change them all to a common denominator of 105
March 14, 2016

Geometry
20 = 4*5 15 = 3*5 LCM(15,20) = 3*4*5 = 60 every 60 seconds one train does 3 laps, and other does 4 laps.
March 14, 2016

solomon mahlangu high
math, computer science, music Now, what are your preferences?
March 14, 2016

maths -quadratic eqn
read up on the discriminant of a quadratic: b^2-4ac
March 14, 2016

Maths
its, not it's in this context. a+17d = 25 since d=2, it is simple to get a. Then, since 49-25=24, and 24/2 = 12, the 18+12=30th term is 49.
March 14, 2016

Maths
huh????? nearest meter means an integer value. What's the integer closest to 9.9?
March 14, 2016

maths
http://www.jiskha.com/display.cgi?id=1457884163
March 14, 2016

Algebra
You just write down what they told you. width: w length: 2w-3 Then you try to remember the way perimeter is calculated. 2(w + 2w-3) = 48 Then you solve for w, and use that to get the length.
March 13, 2016

science
PV = kT. So, PV/T is constant. In fact, since T is constant as well, PV is constant. You want P so that 17.5P = 3*3.5
March 13, 2016

science
given a constant level of energy use, every bit generated from geothermal sources will mean that a similar amount less will be used from fossil fuels. Of course, the relationship is not quite so simple, but that's the general idea.
March 13, 2016

Science
change in speed over time. So, (70-15)m/s / 10min = 4.5 m/s/min Most people feel more comfortable with just two units, so that would be 4.5/m/s/min * 1min/60s = 4.5/60 = 0.075 m/s^2
March 13, 2016

science computer
max = 0 maxname = "" for i=1 to 10   read name,age   if age > max then     max=age     maxname=name   end if next i print "The oldest person is ",maxname
March 13, 2016

algebra
enter your coefficients at the URL below and see all the details. http://www.gregthatcher.com/Mathematics/GaussJordan.aspx
March 13, 2016

Math
since the balls are replaced, the draws are independent events. Just multiply all the probabilities: 5/10 * 3/10 * ...
March 13, 2016

Math
If A's speed is a, then B's speed is a+1 since time = distance/speed, 480/(a+1) = 480/a - 40 a = 3 m/s
March 13, 2016

math
P(t) = -3400 + (4900-(-3400))/4 t = -3400 + 83.25t
March 13, 2016

math
draw a diagram. Review the cotangent function. Then you will see that if the cliff has height h feet, h cot42° - h cot54° = 15
March 13, 2016

Algebra
well, you have 7x = 3y y = 7/3 x 7/3 is the constant of variation. when one says y varies directly with x, it means that there is a constant k such that y = kx If y varies inversely as x, then there is k such that xy = k or, y = k/x These can be combined, so that if you hear y...
March 13, 2016

science
well, since no mass is lost, ...
March 13, 2016

Algebra
y = 1/4 x
March 13, 2016

math
2/5 x - (5/7)(2/5 x) + 62 = x x = 70
March 13, 2016

Trig
AD/sin75° = 100/sin65° AD = 106.58 CD^2 = 50^2 + 106.58^2 - 2*50*106.58 cos50° CD = 83.72 Hmmm. we're close. Better check (a) my math (b) your math On part b, ya got me. what are α and β supposed to be? Maybe they are to be substituted for the actual ...
March 13, 2016

Maths
5a - 5b = 100
March 13, 2016

maths
fix your typos.
March 13, 2016

Math
v varies as r^3. 729 = 9^3.
March 13, 2016

maths
59 = 2+19d Now you can find d. 6th from the end is T15 = 2+14d.
March 13, 2016

math
a = πr^2 + 2πrh so, plug in r=14 and h=35 and do the math.
March 13, 2016

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