Tuesday
September 2, 2014

Posts by Steve


Total # Posts: 24,555

math
7 filled 8 unfilled Choose 6 of each. So, C(7,6) * C(8,6) = ?
June 8, 2014

Math
If two weigh 51, that's the minimum for two boys, leaving the maximum for the 3rd boy of 3*159-2*51 = 159-102 = 57
June 8, 2014

Calculus
dv/dt = 0.6t cos(0.08t^2-1) v = 3/8 sin(0.08t^2-1) + c Since v(0) = 14, c = 14+3/8 sin(1) = 14.3 v(t) = .375 sin(.08t^2-1)+14.3 Now just evaluate v(10)
June 8, 2014

Algebra/could show me how to work this problem
I suspect a typo. Why not just say 2x^2+1? At any rate, assuming things are correct as written, for any input, just substitute it for all the x's and evaluate for the output. input: -2, output (-2)^2+(-2)^2+1 = 4+4+1 = 9
June 8, 2014

Physics-can someone please check this
(b) The horizontal speed is unaffected by gravity, so it remains 24.5 m/s. In 3 seconds, John travels 3*24.5 = 73.5 meters. (a) we know that the vertical position, starting at y0 is y(t) = y0 - 4.9t^2 Since y(3)=0, we can get the initial height by solving y0 - 4.9*9 = 0 y0 = ...
June 8, 2014

Math
wow. cubics are not generally easy to solve. Best bet is a graphical or numerical solution. wolframalpha gives http://www.wolframalpha.com/input/?i=4x^3-6.68E-7x^2%2B1.67E-8x-1.04E-10 The root is very close to zero, since the function is very nearly 4x^3=0 Blowing up the graph...
June 8, 2014

math
lose all the nonsense text. You have (x-1)^2 + (x-2)^2 + (x-3)^2 = 0 Now, you know that (x-1)^2 is a parabola, which is tangent to the x-axis at x=1, because of the double root. Similarly, the other two terms are never negative. So, since we are adding up three positive values...
June 8, 2014

math
you start out talking about two numbers, toss in some unknown quotient (maybe not even in lowest terms) then ask for "number"? The question is mighty unclear to me.
June 8, 2014

Math
just add .145258x to both sides and you have 1.145258x = .145258 now divide by 1.145258 and you get x = 0.126834
June 8, 2014

Doppler Effect
for non-relativistic speeds, we can use the approximation. c/520 = (1+v/c) * c/590 520(1+v/c) = 590 1+v/c = 59/52 v/c = 7/52 v = 7/52 c Is that relativistic? Generally, less than 0.1c is considered non-relativistic, so we may be a bit off, but if that matters, use the exact ...
June 8, 2014

mathematics
The only possible choice assumes a typo where you meant to say that one quarter of x is 36. Then, x is 144. Hmm. Unless the question reads 4 quarters of x is 36. What is 1 quarter of x? Then the answer is 9.
June 8, 2014

science
Assuming you meant 0.400g/dm^3, that translates to 0.0004 g/cm^3 So, 500cm^3 of that means 0.2 g Or, in one step, that's 500 cm^3 * (1dm/10cm)^3 * 0.4 g/dm^3
June 8, 2014

physics
The orbital period is given by T = 2π√(r^3/GM) We want M, which is thus M = r^3/G * (2π/T)^2 Now just plug in your numbers.
June 7, 2014

Maths
Looks to me like they could all be 8. Are there any restrictions on the values allowed? 2014 is not a multiple of 5, so there is no cycle of 5 numbers which repeats.
June 7, 2014

Algebra/not sure what to do
f(x) = x-8 for whatever value x has. So, if x=p, f(p) = p-8 Just replace x with the desired value throughout the entire line.
June 7, 2014

math
I'd say yes. That's what Accounts Receivable are for -- waiting for cash flow to be realized. That's assuming the invoice is not generated until a purchase is confirmed. But, what do I know? I may be off base here.
June 7, 2014

Number Theory
Since the n numbers are divided up in pairs, I'd say n/2 copies. Hence the formula for the sum: n(n+1)/2 Technically, that's [n+1]/2 where [] is the greatest-integer function.
June 7, 2014

maths
If P is x meters from the base of the pole of height h, then h/x = tan 53° h/(x+20) = tan 28° eliminate x and you have h cot 53° = h cot 28° - 20 h = 20/(cot28°-cot53°)
June 7, 2014

math
10(q+7) + 25q = 280
June 7, 2014

Maths
If there are x children, then .6x = 18 x = 30 78? 1? You just throwing darts at numbers? If not, show you r work, so we can help you get it right.
June 7, 2014

math
If we add up terms n through n+10, then we get (n+10)/2 (2a + (n+9)45) - (n-1)/2 (2a+(n-2)45) = 891 11a+495n = -1089 a+45n = -99 If we are adding up the first 11 terms, then a = -144 and T28 = -144+27*45 = 1071 T45 = -144+44*45 = 1836 But, if we add up terms T5 through T15, ...
June 7, 2014

Calculus
Looks good to me.
June 7, 2014

Calculus
x(t) = -cos t + c now you know that x(0) = 3, so plug in t=0 to find c. Then you can use t=2 to get x(2)
June 7, 2014

Maths!
300 = 100 + 40*5 So, set things up as an arithmetic sequence, and find that S41 = 41/2 (100+300) = 8200
June 7, 2014

maths
simple: 10000(1+.12*5) compound: 10000(1+.10)^5 evaluate and compare.
June 7, 2014

calculus
c(x) = 350 + .20 x
June 7, 2014

Algebra
are there any pairs with the same 1st element? If not, it is a function.
June 7, 2014

math
or, using de Moivre's rule, 1+i = √2 cis π/4 so √(1+i) = ∜2 cis π/8 1-i = √2 cis -π/4 so √(1-i) = ∜2 cis -π/8 √(1+i)/√(1-i) = cis π/4 Now the angle doesn't matter, since cos^2+sin^2 = 1
June 6, 2014

math
√(1+i)/√(1-i) = √(1+i)√(1-i) / (1-i) = √(1-i^2) / (1-i) = √2/(1-i) = √2(1+i) / (1-i)(1+i) = √2(1+i)/2 = 1/√2 + 1/√2 i a = 1/√2 b = 1/√2 a^2+b^2 = 1/2 + 1/2 = 1
June 6, 2014

Math
since the slopes are the same, the lines are parallel. Or, in this case, they are the exact same line.
June 6, 2014

Math
Or, knowing that the general circle is (x-h)^2 + (y-k)^2 = r^2 plug in your points to get (-5-h)^2 + k^2 = r^2 h^2 + (4-k)^2 = r^2 (2-h)^2 + (4-k)^2 = r^2 h = 1 k = -19/8 r^2 = 2665/64 and we have the circle as derived above The brute-force way, of course, is to plug your ...
June 6, 2014

Math
The center will lie at the intersection of the perpendicular bisectors of the line segments (chords) joining the points. If we label the points A,B,C, then The midpoint of AB is at (-5/2,2) The slope of the chord AB is 4/5 The line AB is y = 4/5 (x+5) The slope of the radius ...
June 6, 2014

math
-3 + i^2y = -3-y The conjugate of x^2+y + 4i is x^2+y -4i so, we want -3-y = x^2+y - 4i In no case is that ever true We can have -3-y = x^2+y, but there's no way to get the -4i I suspect a typo in the problem.
June 6, 2014

Math
#1. The kth odd number is 2k-1 Think about it : 1,3,5,... #2 It will be a multiple of 60. So, what's the biggest 3-digit multiple of 60? #3 There are 203 numbers from 101-303. Knock off one end, since both are odd, and half of the remaining 202 are even. #4 same thing #5 ...
June 6, 2014

math
2 3/4 = 2 + 3/4 1 1/4 = 1 + 1/4 add them up to get 2+1 + 3/4 + 1/4 = 3 4/4 = 4
June 6, 2014

Write each expression using a single exponent.
when dividing, just subtract exponents: 5^10 / 5^7 = 5^(10-7) = 5^3 because 5^10 = 5*5*5*5*5*5*5*5*5*5 5^7 = 5*5*5*5*5*5*5 divide, and seven of the 5's cancel, leaving only 3 in top: 5^3 76^11 / 76^5 = 76^(11-5) = 76^6
June 6, 2014

wdwd
csc(4θ+3) sin(5θ-6) = 1 That's surely an odd sort of expression. Still, since cscθ = 1/sinθ, we have sin(5θ-6) = sin(4θ+3) So, we want 5θ-6 = 4θ+3 θ = 9 That seems kind of big, so what if we consider that sin(π-x) = sin(x...
June 6, 2014

maths
72000(1+.80n) = 87840 1+.80n = 1.22 and so on to get n
June 6, 2014

math
v = x^3, so dv/dt = 3x^2 dx/dt = 6(2t+1)^2
June 6, 2014

Math
since multiplication is commutative, 3 * 10^6 * 2 * 10^12 = 3*2 * 10^6 * 10^12 = 6 * 10^18 the other is analogous. Just recall that 30*10^13 is not scientific notation.
June 6, 2014

Math
3x^2+2x-x^2+3 3x^2-x^2+2x+3 (3-1)x^2 + 2x + 3 2x^2 + 2x + 3 not much to do -- just combine the x^2 terms. We used commutativity of addition and distributive property.
June 6, 2014

trig
cosA/(1-tanA) + sinA/(1-cotA) cosA/(1-tanA) + sinAtanA/(tanA-1) (cosA - sinAtanA)/(1-tanA) (cos^2A-sin^2A) / cosA(1-tanA) (cos^2A-sin^2A)/(cosA-sinA) cosA+sinA sure you don't have a typo somewhere?
June 6, 2014

trig
since cosA = 5/13, sinA = 12/13 Now just use those values in your double-angle formulas.
June 6, 2014

MATH
wolframalpha.com is your friend. For #26, see http://www.wolframalpha.com/input/?i=table+2x^2-4+for+x+%3D+-3+..+5
June 5, 2014

help needed with math
Was something wrong with the solution I posted here? http://www.jiskha.com/display.cgi?id=1401907573
June 5, 2014

math
4/52 * 4/51
June 5, 2014

MATH
#14. For each x, place a 3. f(3) = 4*3-4*3-7 = -7 Same way for #16 However, I suspect a typo, since 4x-4x-7 = -7 for any value of x.
June 5, 2014

algebra
clearly, 4y = (2/3)x - 8 so, 24y = 4x-48 -4x + 4x-48 = 32 -48 = -32 No solution exists
June 5, 2014

Can you help me find the answers?
#10 14-11*1 = 14-11 = 3 14-11*2 = 14-22 = -8 ... #12 23+1 = 24 23+2 = 25 ...
June 5, 2014

Find the common difference or ratio in each..?
6: r = 1/4 8: r = -2 That should do it.
June 5, 2014

Math
48000(1+.0428/12)^18 = 51,176.82
June 5, 2014

math Study guide
1A 2B 3C 4C 5B Whenever there is replacement, then the events do not affect each other. Or, if the events are unrelated, as with dice and spinners, they are independent. 6: 1/2 * 1/2 = 1/4 7: 1/2 * 3/6 = 1/4 8: 20 total marbles, so 7/20 * 6/20 9: 1/2 * 3/6 (primes are 2,3,5) ...
June 5, 2014

math question check
4/10 * 2/10 = 2/25
June 5, 2014

math
just plug in a value for n and compute the value for C. For example, if 10 people attend, n=10, and C = 10*10+26 = 126 So, the pair for that would be 10,126 Now use your numbers and finish it up.
June 5, 2014

algebra
that's "whether" not "weather". visit wolframalpha.com and just type in a function. It will show you the graph and other information. Be sure to note how interprets you input. You may need to use some parentheses to ensure proper evaluation. The graph ...
June 5, 2014

math question
No, that's 0.15 * 20 Look. 15% means you expect 15 wins in 100 tries. 20 is only 1/5 of 100, so you expect 1/5 as many as 15, or 3. 0.15*20 = 3 That is, 15% of 20 is 3.
June 5, 2014

math question
well, what is .15 * 20 ?
June 5, 2014

math - eh?
Can't say, since you have only presented an approximation to a question. Read what you posted, then supply all the missing data, so we have something to work with.
June 5, 2014

mathematıcal lıteracy
can't say, since you don't say how big the sides are. Also, I assume you mean that 1 litre covers 5m^2 of area. In any case, figure the area to be painted, in m^2, and then multiply that by R26/5m^2
June 5, 2014

Geometery - incomplete
you need to describe the diagram. What is the relationship between the angles? Suppose I ask you what color the fruits are. Have an answer? Also, try using symbols. The usual format is If m<1 = 43°, what is m<2? There is even an angle symbol which you can use: ∠
June 5, 2014

MATH
looks pretty standard to me. To play around with functions and their graphs, you can visit wolframalpha.com and just type in your function. For example, http://www.wolframalpha.com/input/?i=x^2-9
June 5, 2014

math
The usual reference level is 10^-12 W/m^2 Here, you have 2.37*10^-5 W/cm^2 = 2.37*10^-1 W/m^2 The dB level is thus 10 log(2.37*10^11) = 10*11.37 = 113.7 dB
June 5, 2014

Algebra
x^2-144 = (x-12)(x+12) x^2+7x-60 = (x+12)(x-5) 3x-36 = 3(x-12) 9x-45 = 9(x-5) So, since dividing by a fraction is the same as multiplying by its reciprocal, we really have (x-12)(x+12) / (x-5)(x+12) * 9(x-5) / 3(x-12) Now you can see that almost everything cancels out, leaving...
June 5, 2014

Algebra
they all satisfy x-2y = 1
June 5, 2014

Math
the park is 150 by 450, making a perimeter of 1200 ft 1200/10 = 120 seconds G
June 5, 2014

MATH HELP PLEASE & THNX!
revenue = price * demand = pq = p(300000-15000p) cost for q copies is 4q profit = revenue-cost = p(300000-15000p)-4(300000-1500p) = -15000p^2 + 306,000p - 1,200,000 maximum profit is thus at p = 306000/30000 = 10.20
June 5, 2014

Geometry
Just a guess: 3/5?
June 5, 2014

math
solve for x in 150*1.03^x = 300 1.03^x = 2 x log1.03 = log2 x = log2/log1.03 = 23.45 years
June 4, 2014

science
(2^x ln2 - e^x)(2^x+e^x) - (2^x-e^x)(2^x ln2 + e^x) --------------------------------------------------------------- (2^x+e^x)^2
June 4, 2014

science
just plug and chug, using the quotient rule (2^x ln2 - e^x)(2^x+e^x) - (2^x-e^x)(2^x ln2 + e^x) ---------------------------------------------------------------            (2^x+e^x)^2 You can "simplify" that to
June 4, 2014

science
just plug and chug, using the quotient rule (2^x ln2 - e^x)(2^x+e^x) - (2^x-e^x)(2^x ln2 + e^x) ------------------------------------------------------- (2^x+e^x)^2 You can "simplify" that to
June 4, 2014

math
Excuse me? You developed your own function. The price after r rate increases is 6.40 + 0.1r so, for r=0, the price is 6.40 for r=8, the price is 6.40+.1*8 = 7.20 Between those two prices, she'll make at least $1500. Take a look at http://www.wolframalpha.com/input/?i=plot+...
June 4, 2014

math
Your equation looks good. So, just solve it and you get (250-5r) (6.40+0.10r) >= 1500 -.5r^2 - .7r + 1600 >= 1500 .5r^2 + .7r - 100 >= 0 Now, solve the left side using the quadratic formula, and you find that .5r^2 + .7r - 100 = 0 at x = -22.8 and 8.8 Between those ...
June 4, 2014

Delcambre High
r:m = 4/15:1/3 = 4/15:5/15 = 4:5
June 4, 2014

math
well, you know that 1/3 pi r^2 * 8 = 250 So, now just solve for r.
June 4, 2014

math
23010(1+.029/2)^(2*9) = 29816.29
June 4, 2014

math word problem
If he buys x packs of batteries, we wan to find out how many packs it takes to cost more than the price of the charger and batteries. 7x > 15.39 x > 2.2 So, after using the rechargeable batteries 40 times, they will be the better buy.
June 4, 2014

Algebra/not sure what to do Thank You
just pick any value for x and evaluate y at that point. x=0: y=2*0-1 = -1 So the point is (0,-1) x=-5: y=2(-5)-1 = -11 So the point is (5,-11) x=17: y=2*17-1 = 33So the point is (17,33) and so on for any x value you want. You can also pick y, but then you have to work ...
June 4, 2014

geometry
Can't tell. The two bases are equilateral triangles, but the three lateral faces are rectangles of area 6. But is the prism tall and skinny, or short and fat? You must know either the height of the prism, or the side length of its bases. If the bases are of side 2s, then ...
June 4, 2014

Trig
55° + 360k are all coterminal for any integer k. 9/5 π + 2kπ are all coterminal for any integer k. So, pick a positive and negative k
June 4, 2014

math(log)
since 81 = 3^4, we have 3^-4 = 3^(2x-1) -4 = 2x-1 x = -3/2 logx + 3/logx = 4 log^2(x) - 4logx + 3 = 0 (logx-1)(logx-3) = 0 logx = 1,3 x = 2,8 check: 1+3/1 = 4 yes 3+3/3 = 4 yes
June 4, 2014

Math
us always, draw a diagram. Label one of the acute angles θ. The side opposite is 4 and the side adjacent is 3. (Note: the hypotenuse is not a side!) The hypotenuse is 5, since 3^2+4^2=5^2 Now, review your trig definitions. sinθ = opposite/hypotenuse = 4/5
June 4, 2014

geometry
sin 40° = x/80
June 4, 2014

math
sin 70° = 25/x As usual for trig problems, draw a diagram. In this case, label the angle at the ground 70°. You want the hypotenuse (x), and have the side opposite the angle (25).
June 4, 2014

math
Not sure what "compounding amount" means. If you mean the final amount after adding the interest, just apply the usual formula, which you surely have. A = 700(1+.015/12)^(12*8) = 789.19 To find just the interest, subtract the original $700, leaving just $89.19
June 4, 2014

maths
if the bot has speed b, and the stream has speed s, then since time=distance/speed, 12/(b-s) + 40/(b+s) = 8 16/(b-s) + 32/(b+s) = 8 b=6 s=2 check: 12/4 + 40/8 = 3+5 = 8 16/4 + 32/8 = 4+4 = 8
June 4, 2014

math algebra?
You forgot the minus sign. -4p < 36 p > -9 That's just shorthand for switching sides of the inequality: -4p < 36 -36 < 4p -9 < p
June 4, 2014

maths
3000/(pi*75) = ?
June 4, 2014

10
What happens if the square does not share sides with the triangle? If the vertices of the triangle are at (0,0),(6,0),(0,12), then if one side of the square is on the hypotenuse, and one corner is at (s,0), another is at (0,2s), so the hypotenuse has length √5 s. Now, we...
June 4, 2014

trig angle of elevation
The rim is only 4 feet above his eyes, so 4/x = sin 12.5° we don't really care how far horizontally he is from the basket. All that stuff about 15 feet and stepping back is just noise. The final picture is just a 12.5° angle with a 4-ft height difference.
June 4, 2014

Math please help
don't let those fractional exponents confuse things. What you have is just (x^1/5)^2 + x^1/5 - 6 = 0 That's just like u^2+u-6=0 So, just factor it to be (x^1/5 + 3)(x^1/5 - 2) = 0 x^1/5 = -3 or 2 x = -243 or 32
June 4, 2014

Math
18% compounded 12 times per year give 1.5% per month. So, 6 years = 72 months.
June 3, 2014

MATH
3(x+2) = 3*x + 3*2 = 3x+6 an identity 3(x+4) = 3*x + 3*4 = 3x+12 ≠ 3x+4 not only not an identity, but not even conditional. There is no value of x which makes it true!
June 3, 2014

math
√32 = 4√2, so we have 4x*4√2xv^2 + v√2x^3 16x√2x√v^2 + v√2x√x^2 16xv√2x + vx√2x 17vx√2x
June 3, 2014

math
2:3 = 4:6, so draw the picture with 4 pencils and 6 pens
June 3, 2014

Math
38*34 = 1292 you are correct
June 3, 2014

math
var=25 means std=5 113 is 12 below the mean, or 2.4 std So, what's P(Z < -2.4)
June 3, 2014

Math
5^1 * 5^10 5^5 * 5^6 5^20 * 5^-9 In each case the sum of the powers is 11.
June 3, 2014

Algebra
f(n) = 10(1.02)^n A: since f(0) = 10, we're looking for a growth of 11.04/10 = 1.104 1.104/.02 is about 50, so as a rough guess I'd go with a domain of [0,50]. B: y-intercept is the initial population (when n=0) C: (f(5)-f(1))/(5-1) = 0.21 Represents a constant growth ...
June 3, 2014

ly and solve for x.
try something simple, like 3 = x/2 You want x all alone, so get rid of that pesky fraction. Since 2/2 = 1, multiply both sides by 2 and you get 3*2 = x/2 * 2 6 = x Now, for your problem: 8/18 = x/225 You can clear the fraction on the left by multiplying by 18. 8/18 * 18 = x/...
June 3, 2014

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