Monday
September 15, 2014

Posts by Steve


Total # Posts: 24,918

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

Choose the term to complete this sentence?
hmmm. I don't see any mention of a proposed experiment, so ...
June 3, 2014

Geometry
area of sector is 60/360 * 81pi arc length subtended is 60/360 * 18pi For any other questions, you're on your own...
June 3, 2014

Pre-Algebra
Just use the distributive property: n(n-1)-4 n*n - n*1 - 4 n^2-n-4 Since f(x) = x^2-4x+3, and you want f(-3), just replace all the x's with -3 and you have f(-3) = (-3)^2 - 4(-3) + 3 = 9+12+3 = 24
June 3, 2014

Algebra 1 (Reiny)
#1 no solution #2 ok #3 ok but I had to try two different ways of inserting parentheses before I got your answer. Grrr. The spacing in "t + 2" was especially deceptive. #4 x = 0 or 2 This time, overkill. Use parens as needed, but only as many as it takes to avoid ...
June 3, 2014

Algebra 1
since the denominator is the same on both sides, just work with the numerators: d+2 = -6 d = -8 BZZZT! But thanks for playing. Since the denominator is d+8, d = -8 is not in the domain, because that would cause division by zero. Before clearing fractions, be sure to note which...
June 3, 2014

Algebra 1--Please, check my answer!
You can go overboard with the parentheses. In this case, there's no confusion if you just write 1/x = 2/x^2 so, x/x^2 = 2/x^2 x = 2 check: 1/2 = 2/4 yes
June 3, 2014

Algebra 1--Please, help me!
(4x-3)^2 = 16x^2 - 24x + 9 You have -9. A perfect square will never end in a negative number.
June 3, 2014

calculus
add the two vectors and you get <539,0> + <43,43> = <582,43> arctan(43/582) = 4.2° As a bearing, that's E 4.2° N, or 85.8°
June 3, 2014

Algebra 1
work with the amount of orange juice in each container. If x cups of 100% orange juice are added to 8 cups of 25% orange juice, she will wind up with x+8 cups of 40% orange juice. .25*8 + 1.00*x = .40(8+x) x = 2 check: There are 2 cups of oj in the 8 cups of 25% mix There are ...
June 2, 2014

Math
sure. Two intervals that overlap at a single point. x+y >= 3 2x-3y <= 1 y <= x/2 The single point which satisfies all three equations is (2,1)
June 2, 2014

geometry
If the smaller diameter is d, the other is d+8 d + d+8 = 28 Now just find d, and figure d+8.
June 2, 2014

Calculus
for polar coordinates, dA = 1/2 r^2 dθ since each tiny wedge of area can be considered a sector of a circle of radius r and angle dθ. So, since r = 8+4sinθ, a = ∫[0,2π] 1/2 (8+4sinθ)^2 dθ now just expand the quadratic and evaluate each term...
June 2, 2014

physics
If the positive direction is east, we have to add up the two velocities: 395 - 55 = 340 or, 340km/h east
June 2, 2014

Algebra 1
since time = distance/speed, 12/s - 1 = 12/(s+1) Hint: 3 is one less than 4.
June 2, 2014

algebra - incomplete
no idea - how long did it fly?
June 2, 2014

Algebra
#1 If the sides are x and y, then x^2+y^2 = 68^2 (not √68) xy = 16 so, y = 16/x x^2 + 256/x^2 = 68^2 x^4 - 68^2 x^2 + 256 = 0 since 256 = 4*64, we have (x^2-4)(x^2-64) x = 2 or 8 (discard the negative roots) #2 If the cardboard is of side x, then (x-8)(x-8)4 = 784 x^2 - ...
June 2, 2014

Algebra/very confused
If you mean square root, use √ and some parentheses. Do you mean 3 ln e = √(7x) - 3 ln 6 ?? If so, recall that ln e = 1 3 ln 6 = ln 6^3 I still doubt that's what you want. It still looks bogus.
June 2, 2014

Math
those double minuses make a +, so you really have -39+24+64 leading minus signs make some people uncomfortable, so bob moved it to the end.
June 2, 2014

Algebra - Math HW HELP!
just work with the clues. The number's digits are abcde palindrome means it is abcba tens digit must be 1 or 2, so b=1 or 2 a2c2a a1c1a c*a = 54, so c=9 and a=6 or vice-versa 92629 62926 91619 61916 c+a=15 well, we already knew that with the 9 and 6 divisible by 4 knocks ...
June 2, 2014

Math algebra
Assuming a $26 budget per table, you have 8 favors and 8 flowers. The 8 flowers cost 8*2.50 That leaves for the favors, cost = (26-8*2.50)/8 Better be cheap favors! And if your total budget is $26 for all the tables, forget it, since the flowers for a single table already cost...
June 2, 2014

math
10% = 1/10 So, it rises 1/10 as far as it runs horizontally: .2km or 200m
June 2, 2014

Calculus Help
It might be helpful to rescale things by letting u = (x-30)/30 so the u-values go from 0 to 5. Then, since we are expecting an exponential relationship, see whether you can find something that fits ∆y/∆u = ky + c See where that takes you
June 2, 2014

math
No reason to stop there. Factor out all those 3's: 81(x^2+1)(x-1)(x+1) If you must pick one of those choices, then use the last one, since it factors the 9x^2-9 as well. (factor completely!)
June 2, 2014

algebra 2
if the tortoise is last, then you just have to worry about the other 5 animals. So, in how many ways can you arrange 5 things?
June 2, 2014

algebra
If the vertex of the parabola is at (0,630), then the arch is modeled by y = (630/315^2)(315^2-x^2) = 630 - 2/315 x^2 If the work is being done at a position c ft to the right of the vertex, it will be at the point (c,y(c)), on a line with slope 1/5. Unfortunately, this makes ...
June 2, 2014

math [linear equations]
If you can plot points, remember that two points determine a line. So, pick two easy points and plot them. Then draw a line through them. So, what's easy? How about letting x=0 or y=0? That gives us 0-y=5 y = -5 x-0=5 x=5 So, our two points are (0,-5) and (5,0) Now it ...
June 2, 2014

College Algebra
Excuse me? You already know that the length is 20 more than the width. So, if the width is 80, the length is 100. Sure enough, 80*100 = 8000 Or, since you know the width is 80, and area = length*width 8000 = 80 * length length=100 Don't forget your algebra I now that you&#...
June 2, 2014

geometry
Trying to match the question with the choices sure stumps me. Using similar triangles, if we label the vertices of the triangle P,K,F, and the library L, then we have ∆LPF ~ ∆KLP we want the distance LP and FP, and we have LP/2 = FP/KP LP/8 = KP/FP so, LP/2 = 8/LP ...
June 2, 2014

Math Helppp
you can play around at http://davidmlane.com/hyperstat/z_table.html and do all kinds of neat Z-table stuff. Just enter your mean and std and you can see the areas (probabilities) for various kinds of calculations.
June 2, 2014

math
#1 ok, though I'd write it as 4.00t + 25.00 Lose all that "x" stuff, if for no other reason than because "x" is often used as a variable. "*" is better for explicit multiplication. #2 where did 350 come from? If t shirts are ordered, then t of...
June 2, 2014

math problem
the slope of the line is ∆y/∆x, so m = 6/7 Now you have a point and a slope, so the line is y-4 = 6/7 (x-0) or y-10 = 6/7(x-7) and you can massage them to whatever form you like, and convince yourself that they are really the same equation.
June 2, 2014

math
the fifth-root of x^20 is (x^20)^(1/5) = x^(20 * 1/5) = x^4 Because (x^4)^5 = x^20 Roots are just fractional powers.
June 2, 2014

math 1 question!!!!!!
I think I'd go with a line plot. Each column will indicate how many days have a particular number of calls. The mode will be the tallest column. Plotting with time intervals could produce the same information, but would require more analysis.
June 2, 2014

trig
you cannot draw it here. However, you can see them here: http://www.wolframalpha.com/input/?i=plot+y%3Dtan%28x%29%2C+y%3D2cos%28x%29+for+x+%3D+-pi..pi x is in radians, but the graphs look the same for degrees: http://www.wolframalpha.com/input/?i=plot+y%3Dtan%28x*pi%2F180%29%...
June 2, 2014

Math
Twenty tires are tested to see if they last as long as the manufacturer claims they do. Three tires fail the test. Two tires are selected at random without replacement for an inspection. Find the probability that both tires fail the test. Which is greater, the probability that...
June 2, 2014

Trigonometry, can someone check this please
money is no excuse. you evidently have the internet. A simple google search will provide oodles of explanations and examples. One key fact, which I found one of my students was having trouble with: For the purposes of the trig functions, the hypotenuse is not a side! When ...
June 2, 2014

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