Friday
February 12, 2016

Posts by steve

Total # Posts: 37,589

math
Because y(0) = 0. It helps if you actually read what I write. Or maybe it has something to do with the mysterious "a".
December 27, 2015

math
well, f'(x) = cos(√2 x) - √2 x sin(√2 x) Not sure what a has to do with things, but if you meant x=0, then f(0) = 0 f'(0) = 1 So, you want the line with slope 1, which passes through (0,0). No too much of a challenge there, eh?
December 27, 2015

math
cancel what out? There are no common factors.
December 27, 2015

math
well, the 1st three terms are 2^2, 3^3, 4^4, so what's your best guess?
December 26, 2015

Maths
42a
December 26, 2015

physics
As I recall, the force grows as the ratio of the areas of the pistons. That means, as the square of the diameter. So, since 6 = 3*2, the force would be 3^2 * 20 Review your text on this subject. I'm sure there are examples. And you can always rely on google for lots of ...
December 26, 2015

Calculus
rearranging things a bit, we have y' = y(t+1) + t+1 y' = (y+1)(t+1) dy/(y+1) = (t+1)/t^2 dt ln(y+1) = ln(t) - 1/t + c y+1 = t e^(-c/t) + c2 or, altering the c values, y = ct e^(-1/t) + c2 y(1) = 0, so 0 = c/e + c2, so c2 = -c/e y = c(t e^(-1/t) - 1) We can ignore the c...
December 25, 2015

Math
how about if we start by saying y-1 = 3sin((1/2)(x+pi)) and y+2 = -1/3 cos(2(x - pi/2)) the shifts and scalings should now be clearer.
December 25, 2015

math
There are infinitely many chords passing through any point within the circle. Two such chords, easy to describe are x=2 and y=3.
December 25, 2015

Statistics
18 rings total, so that would make the probability 10/18 * 9/17
December 25, 2015

math
There are infinitely many chords passing through any point within the circle. Two such chords, easy to describe are x=2 and y=3. ---------------------------------------- Clearly, the vertex of the triangle is at (0,5), so the altitude is 3. The base of the triangle goes ...
December 25, 2015

math
Draw diagonal BD Then triangles ABD and CBD are isosceles. Hence, their altitudes bisect their bases and their vertex angles.
December 25, 2015

physics
54.45 mph = 79.86 ft/s If the rock was thrown with an initial speed k, then k-32*2.75 = -79.6 k = 8.4 ft/s So, the rock was thrown upward at 8.4 ft/s from a height h: h - 32*2.75 - 16*2.75^2 = 0 h = 209 ft
December 25, 2015

mathematics
(x-1)(x-2)(x-k) = x^3 - (k+3)x^2 + (3k+2)x - 2k k+3 = p 3k+2 = 2 q = -2k Looks like k=0, so p=3 q=0 and we have x(x-1)(x-2) = x^3 - 3x^2 + 2x
December 25, 2015

maths
or, using partial fractions, 2 - (5/9)/(x+2) - (13/9)/(x-1) + (1/3)/(x-1)^2
December 25, 2015

Trigonometry- ??????
oh come on. If ab=0, then either a=0 or b=0 So, we have tanx = 0 --> x is a multiple of pi or sin^2(x) = 2 --> no solutions there.
December 24, 2015

Trigonometry- ??????
tan(x) sin^2(x)=2tan(x) tanx(sin^2(x)-2) = 0 How about now?
December 24, 2015

Algebra 1
39.80x + 49.70y <= 150,000
December 24, 2015

Math
looks good to me. or, you could have noted the 41-22 = 19%, and that would be 76.
December 24, 2015

math
the units would be dollars/yd^2 The rate of change is always ∆y/∆x, so the associated units just follow along. y might be the cost (dollars) of some quantity x (yd^2) of carpet.
December 24, 2015

Calculus
u = sinx du = cosx dx so, dx = du/cosx = du/√(1-u^2) sinx(cosx)^2 dx = u(1-u^2)/√(1-u^2) du = u/√(1-u^2) du Now, let v = √(1-u^2) dv = -u/√(1-u^2) du and you have -v dv integrate that to get -1/2 v^2 = -1/2(1-u^2) = -1/2 (1-sin^2(x)) = -1/2 cos^2(...
December 23, 2015

Calculus
because now we are using u, not x. If, after integration on u, you substitute back into terms of x, then you would use the limits [0,2]. When x=0, u=3 and when x=2, u=5.
December 23, 2015

Calculus
∫[0,2] x√(5-√(4-x^2)) dx Let u = 5-√(4-x^2) du = x/√(4-x^2) dx so, x dx = (5-u) du and you now have ∫[3,5] √u (5-u) du and I'm sure you can handle that, eh?
December 23, 2015

Math
n is starting population. t is time period k indicates how fast it grows. To use it, um, just plug in your numbers... Surely, knowing the formula, you have examples of its use. If not, google is your friend.
December 23, 2015

Algebra 2
you have the sum of two cubes, so it factors into (3x+5)((3x)^2-(3x)(5)+5^2) = (3x+5)(9x^2-15x+25) It's easy to check that the quadratic has no real solutions. Just use the quadratic formula, learned long ago in Algebra I...
December 23, 2015

MATH Please help!
if the dimensions increase by a factor of 3, the area increases by a factor of 3^2, so A is correct. 13^2 * 3^2 = (13*3)^2 = 39^2
December 23, 2015

math
domain is positive integers range is (0,N] where N is the maximum time for a single painter. Further restrictions depending on the maximum number of painters, and other information on their required times.
December 22, 2015

math
clearly, the mass depends on the number of candies, which is an easily controlled integer value.
December 22, 2015

Gwu
I think that is supposed to read and spends it takes .75mi * 1hr/2mi = .375hr = 22.5 min to travel between stops. So, assuming we start counting as the train arrives at the 1st intersection, it takes (in minutes) 12*.75 + 11*22.5 = 256.5 minutes before it leaves the final ...
December 22, 2015

SCIENCE
surely it would have taken less time just to look in your text, or google, rather than post here and wait.
December 22, 2015

Algebra
Note that y increases by 4 when x increases by 1. So, the slope is 4. That should help.
December 22, 2015

metreology
just review the wavelengths for the parts of the spectrum.
December 22, 2015

chemistry
google is your friend. Try it. Many discussions.
December 22, 2015

Happy Christmas and Merry New Year!!
Happy RamaHannaKwanzMas!
December 22, 2015

Algebra 2
Since tan(x) has a midline of y=0, and this is shifted down 4 units (due to the -4 at the end), so is the midline: y = -4
December 22, 2015

maths, physics,
Maybe if you show your work, you can learn where you went wrong.
December 22, 2015

maths, physics,
unless otherwise denoted, such as S20°E, headings are indeed clockwise from north. So, the plane (apparently aka helicopter)'s velocity is 400<0.939,0.342> and the wind is 70<-0.707,0.707> <326.11,186.29> = 375.568 at 60.3°
December 22, 2015

Science
this is just the usual 30-60-90 right triangle, with hypotenuse 100. Now just find the sides.
December 22, 2015

victoria university college,Myanmar,mechanical pri
No idea. How many kW does the machine use? Then just multiply by 7 to get kW used and then multiply by $.08 to get cost
December 22, 2015

math
what a deal! Oh - was there a question in there somewhere?
December 21, 2015

statistics
This just like drawing without replacement, so your probability is 8/25 * 7/24 = 7/75
December 21, 2015

pharmacy tech
or just use the 5% solution and add water. Since 3% is 3/5 of 5%, just use 3/5 of the 30mL and fill the rest with water: 18 mL 5% + 12 mL water Or, for a much slower method, pour some 1% solution in a beaker and let it evaporate. Since 1% is 1/3 as much as 3%, start out with 3...
December 21, 2015

geomtery
You know the three angles sum to 180, so 3x+9 + 8x+11 + 5x-8 = 180 16x + 12 = 180 ... Now you can find x, and thus the three angles.
December 21, 2015

Algebra
since the coefficients of x and y are the same, yes they are parallel.
December 21, 2015

statistics
you can play around with Z table stuff at http://davidmlane.com/hyperstat/z_table.html
December 21, 2015

math
since time = distance/speed, time out = d/5 time back: d/3 avg speed = total distance / total time = 2d/(d/5 + d/3) = 2/(1/5 + 1/3) = 2/(8/15) = 15/4 Close to 4, but not quite.
December 21, 2015

maths
4/3 π r^3 = 1/3 π r^2h 4r = h ...
December 21, 2015

maths
the ratios are πr^2h : π/3 r^2h : 2π/3 r^3 = πr^3 : π/3 r^^3 : 2π/3 r^3 I expect you can take it from there. Just factor out the common values and clear the fractions as needed.
December 21, 2015

maths
If the three roots are r,s,t then their product rst = c/a. So, if r = -1, then st = = c/r = c/-1 = -c.
December 21, 2015

math
I have an idea. Why don't you give it a try. To start with, 2 is a factor of any even number...
December 21, 2015

math
I hope -4x-31 is one of the choices. That would be easiest. Of course, there are many many other equivalent expressions...
December 21, 2015

maths
any number whose digits sum to a multiple of 9, is divisible by 9. So, ...
December 21, 2015

our own English school
By an even multiple of 2, do you mean a multiple of 4? As in 6 is an odd (3) multiple of 2, but 24 is an even (12) multiple of 2? In any case, just pick any multiple of 2 or 4, as required, whose digits sum to 9. Such as 72, 234, 69732, etc. Read about "casting out nines&...
December 21, 2015

Math
by now surely you know that |<a,b>| = √(a^2+b^2)
December 21, 2015

Algebra
Eh? I've never seen an or written like that... It's always been in two parts: x < -5 OR x > +5
December 21, 2015

mathamatic
Some of these are simple arithmetic or geometric sequences. Other are easily recognizable powers, such as n^2 or 2^n, or are Fibonacci-like. Why not take a shot at them and let us know what you come up with?
December 21, 2015

mathematics
No idea. You have a mish-mash of notations. Try using the most common online one: ^ for power, as in 12araisedto Power3b = (12a)^(3b) and so on for your others.
December 21, 2015

mathematics
If the son is x, the father is 5x. So, x + 5x = 78 ...
December 21, 2015

vectors
well, you know that you need 2^2+1^2+x^2 = 1 good luck with that, since x^2 is always positive. I suspect there is more to this problem than you posted.
December 21, 2015

vectors
A = <1,1,2> You want B = <a,b,c> such that A•B = a+b+2c = 0 Should not be hard to figure out some values, such as <1,1,-2> or <3,5,-4>
December 21, 2015

Math
If there was $x at 3%, then the rest (10000-x) was at 6%. Now just compare the two amounts, and find x: .03x + 357 = .06(10000-x)
December 20, 2015

math
so, who said y is an integer?
December 20, 2015

math
rearrange things a bit to get 2x + 3y = 7 x - 2y = 4 Now double the 2nd equation and you have 2x + 3y = 7 2x - 4y = 8 Now subtract and you have 7y = -1 And your way is clear...
December 20, 2015

Math
set up the equations just as I did, using your new numbers.
December 20, 2015

Math
L/J = 4/3 L = J+10 Hmmm. Looks like 40 and 30, huh?
December 20, 2015

Physic
suppressing all those units, we have (.300)(4190)(T-70) + (.100)(390)(T-20) = 1257T - 87990 + 39T-780 = 1296T - 88770 You can do with that what you will
December 20, 2015

Geometry
congruent to what?
December 20, 2015

geometry
nope. try again.
December 20, 2015

math help pls pls
just add the two equations, and you have 3x = 9
December 20, 2015

MATH HELP
correct
December 20, 2015

MATH HELP
You know it is a line. Now just try the points in (a) and (b). Do they satisfy the equation?
December 20, 2015

MATH HELP
geez. did you actually check the numbers? They clearly work for (d).
December 20, 2015

Physics
42°
December 20, 2015

math
Clearly there were 4 3-pointers and 9 2-pointers. You don't even need the total score for that, since two numbers sum to 13, and one is 5 more than the other. TMI
December 20, 2015

Physics 1st
just use your formula for length contraction. as you recall, it will contract by a factor of √(1-.49)
December 20, 2015

Calculus i need help
or, we might go at it using logs: y ln(cos(x)) = sin(y) ln(x) Now all we have to worry about is the chain rule and product rule: ln(cos(x)) y' - y tan(x) = cos(y) ln(x) y' + sin(y)/x y' = y tan(x) + sin(y)/x ------------------------------ ln(cos(x)) - cos(y)ln(x...
December 20, 2015

Calculus i need help
(cosx)^y = x^siny As you recall (or can work out yourself with little effort) the derivative of u^v where u and v are both functions of x, is just a generalization of the power rule and the exponential rule: y = u^v y' = v u^(v-1) u' + ln(u) u^v v' Note that if u ...
December 20, 2015

Maths
just enter your expressions in the box at wolframalpha.com and it will show you the partial fractions decomposition. Be sure to include enough parentheses that your input agrees with wolframalpha's interpretation of it.
December 20, 2015

Maths
what do you mean by a "constant" equation?
December 20, 2015

math
If the cost is x, .93x = 31 x = 33.33 Profit at Rs 35 = 1.167 = 3.5%
December 20, 2015

Maths
Use matrices or determinants. How far do you get?
December 20, 2015

maths
If you consider that LCM(2,3)=6 a = x^4/y^3 b = y^2/2x You want terms of the form a^2b^3 or a^4b^6, ... Since we have a 10th power expansion, the exponents must add to 10, so we are looking for a^4b^6. That is, the 5th term: C(10,4) a^4 b^6 = 210 x^16/y^12 y^12/64x^6 = (105/32...
December 20, 2015

Maths
I'm sorry -- I mussed have missed the memo. What was the question?
December 20, 2015

Partial fraction
Since both factors in the denominator are irreducible quadratics, each numerator will have the form of (Ax+B) I get (1/10)(x-3)/(x^2+1) + (1/10)(7x+5)/(3x^2+4x+5)
December 20, 2015

Maths
you solve an equation. I don' see no steeking equation. All you have is an expression. What do you want to do with it?
December 20, 2015

maths
From the timing at 3:00, we see that the intervals are 15 seconds long. 12:00 is 12 strikes, but only 11 intervals.
December 20, 2015

math
Better check your math. The markup is not 36%, since the 10% discount also applies to part of the markup. Try some actual numbers.
December 20, 2015

math
If there is a markup of m, then we have (1+m) * .90 = 1.26 m = 0.4, or 40% Draw the chord, and a radius which bisects it, and the radii to the two ends. Then you will note that you have two 3-4-5 right triangles. So, the chord length is 6.
December 20, 2015

Maths
Assume the base is along the x axis. Assuming the vertex is between the ends of the base and has x-coordinate v, then if the two sides have equations y = mx+n and y = hx+k, then just integrate ∫[0,v]∫[0,mx+n] dy dx + ∫[v,a]∫[0,hx+k] dy dx If v is not ...
December 20, 2015

St. Vivekanand sr. sec. school,bikaner
assuming you mean i = √-1, then since i = 1 cis π/2, i^i = 1 cis (π/2 i) = cos(π/2 i) + i sin(π/2 i) = cosh(π/2) - sinh(π/2) = e^(-π/2)
December 20, 2015

calculus
clearly, we want f'(x) = 3ax^2 + 2bx + c to be zero at x= -5 and 4. So 3ax^2 + 2bx + c = k(x+5)(x-4) = kx^2+kx-20k so, c=-20k, 2b=k, 3a=k and f(x) = (k/3)x^3 + (k/2)x^2 - 20kx + d f(4) = 64k/3 + 8k - 80k + d = -152k/3 + d = -4 f(-5) = -125k/3 + 25k/2 + 100k + d = 425k/6 + ...
December 19, 2015

Math
y > 3x+10 y < 3/4 x - 1 So, graph the two lies. Shade the area above the first line, and below the 2nd line. Use dotted lines. (why) Does (8,10) fit both inequalities?
December 19, 2015

Trigonomentry plz help
taking reciprocals, we have cot^2A = 1/n^2 cot^2B csc^2A = 1/m^2 csc^2B m^2 csc^2A - n^2 cot^2A = csc^2B-cot^2B = 1 Now you should be able to get things down to cos^2A
December 19, 2015

Trigonometry- ??????
to explain, just evaluate: |a| = √200 |b| = √41 a+b = (14,15) |a+b| = √394 19.85 |a|+|b| = √200+√41 = 20.55 Seems clear to me. if a and b are two sides of a parallelogram, a+b is the diagonal. Clearly the indicated values cannot be equal unless a ...
December 18, 2015

Math
490 * 1.11^10
December 18, 2015

Tech
what do you mean by "the pitch"? An audio file contains many pitches. You want the whole file to be a single frequency at a constant volume?
December 18, 2015

Math
well, I'd guess that would be 1/2 of 2/3 So, what's 1/2 of 2? Take that many "thirds"
December 18, 2015

algebra
how about: what percent of 2 is 1? How did you get that? Do the same with 7 and 21.
December 18, 2015

algebra
Just read what it says, and write it down in symbols: If we start out with x = Rudolph's bells y = Dasher's z = Dancer's after step 1 we have x-y-z 2y 2z After step 2 we have 2(x-y-z) = 2x-2y-2z 2y-(x-y-z+2z) = 3y-x-z 4z After step 3 we have 4x-4y-4z 6y-2x-2z 4z-(...
December 18, 2015

Math
100,000,000*(1+.045)^2 I suggest you try investing $1000 first.
December 18, 2015

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