Monday

May 25, 2015

May 25, 2015

Total # Posts: 31,386

**Math 115**

If the cheap sides are x, and the expensive side is y, then xy = 320 c(x) = 6*2x + 6y + 14y = 12x+20y = 12x + 20(320/x) c'(x) = 12 - 6400/x^2 minimum cost is at x = 80/√12 ≈ 23 So, the area is roughly 23 by 14 (That's 322 ft^2)
*March 26, 2015*

**Math 115**

P = R-C that will be a parabola. Find its vertex.
*March 26, 2015*

**Math**

Look. If I said I had to pick 10 apples, but I only had 7 so far, how would you decide the number I still needed? Don't let the fractions scare you. They're just numbers.
*March 26, 2015*

**Math**

subtract what he has from the total.
*March 26, 2015*

**math**

f(x) = cx/(2x+3) f(f) = cf/(2f+3) = c[cx/(2x+3)]/(2[cx/(2x+3)]+3) = c^2x/(2(c+3)x+9) So, if c^2x/(2(c+3)x+9) = x, c^2x = 2(c+3)x^2 + 9x 2(c+3)x^2 + (9-c^2)x = 0 x(2c+6+9-c^2) = 0 x(15+2c-c^2) = 0 x(5c-1)(3c+1) = 0 So, c = 1/5 or c = -1/3
*March 26, 2015*

**Algebra**

f(x) = 2(x-1)^2 - 7 So, if we restrict the domain to x>1 or x<1 we can find an inverse
*March 26, 2015*

**math**

h = 1/√x h^2 = 1/x x = 1/h^2 so, h^-1(x) = 1/x^2 h^-1(4) = 1/16
*March 26, 2015*

**algebra**

since g(x) is a parabola, there are two values of x for every value of g. So, there is no inverse. However, if you pick a single branch of the parabola (that is, you restrict the domain), there is an inverse.
*March 26, 2015*

**Math**

Convert 22 miles to yards. Use a proportion to solve. Show your work. Where do I start with this problem?
*March 26, 2015*

**calc**

f is a polynomial, so it is continuous and differentiable f(4) = f(0) = 8, so that's ok So, you want c where f'(c) = 0 That means you need 3c^2 - 2c - 12 = 0 c = 2.361 The other value is not in [0,4]
*March 26, 2015*

**Math**

starting from M, you go 74 SE and 42 W That is (52.33,-52.33) + (-42,0) = (10.33,-52.33) tanθ = -52.33/10.33 = -78.8° So, the bearing is 168.8° or E 78.8° S or S 11.2° E
*March 26, 2015*

**5th grade math**

80 <= 1.22n <= 85 divide through by 1.22 and you get 65.57 <= n <= 69.67 If you want only integer values for n, then that would be any of 66,67,68,69
*March 26, 2015*

**geometry**

not sure how I'd do it without trig. Any clever geometric relationships that make it easy?
*March 26, 2015*

**geometry**

in triangle PQS. sinP/9 = sinQ/8 = sinS/5 So, you can find angle P Now, using the law of cosines in triangle PRT RT^2 = 10^2 + 16^2 - 2*10*16*cos(P)
*March 26, 2015*

**calculus**

p(8) = 1536 p(4) = 192 so, avg v is (1536-192)/(8-4) = 336 p'(t) = 9t^2 so, you want 9c^2 = 336
*March 26, 2015*

**7th grade math (probability)**

They all look good to me.
*March 26, 2015*

**math**

Huh? You said above what the vertex is. as always, it is at t = -b/2a It is not at t=3, but very close. Probably good enough.
*March 26, 2015*

**math**

clearly there is an x-intercept somewhere just beyond 6. See how the height is descending. Since the given h values do not show an obvious symmetry, it is not immediately clear where the vertex is. However, since h(0) = 0, if h(t) = at^2 + bt + c c = 0, so h(t) = at^2 + bt ...
*March 26, 2015*

**math**

try writing fractions like this: 2/3 + x/4 = 4/7
*March 26, 2015*

**Algebra**

two real roots
*March 26, 2015*

**Math**

well, just work from the inside out 2/3 - 1/3 = 1/3 so, what you have without the brackets is 1/3 * 5/8 = 5/24
*March 26, 2015*

**Math**

1 yd = 3 ft (1 yd)^3 = (3 ft)^3 = 27 ft^3
*March 26, 2015*

**Algebra 1**

(66-6)/6 = 10 (77-7)/7 = 10
*March 26, 2015*

**^math^**

√(19-4√21) since 21 = 19+2, I'd check (2-√21)^2 = 4-4√21+21 nope (1-2√21)^2 = 1-4√21+42 nope (2√3-√7)^2 = 12-4√21+7 aha!
*March 26, 2015*

**MATH**

.08x - .05(36000-x) = 2750
*March 26, 2015*

**algebra**

simple interest, yes compound interest, no
*March 26, 2015*

**math**

didn't my solution in the related question below do the job?
*March 26, 2015*

**math**

-3 It helps a bunch if you use a caret (^) to indicate exponents. As in (10^6)^-3 = 10^-18
*March 26, 2015*

**science**

1st step: figure how many moles of each you have. Then figure the fraction.
*March 26, 2015*

**math**

well, you know the formula for the area of a triangle, so plug in your numbers 30h/2 = 600
*March 26, 2015*

**algebra**

for substitution, I would, um, substitute. The 1st equation tells you that y = -2x So, substitute that into the 2nd equation to get x-3(-2x) = -7 x+6x = -7 7x = -7 x = -1 Now you can find y. As for elimination, 3x + 4y = 1 5x – 3y = 21 to eliminate y, multiply the 1st by ...
*March 26, 2015*

**Geometry**

just solve 2(3x+10 + x+12) = 76 then you can figure the length and width, and thus the area.
*March 26, 2015*

**math**

see related question below
*March 26, 2015*

**Math**

just as you would any quadratic: 1.862t^2 - 50t - 2 = 200 1.862t^2 - 50t - 202 = 0 t = (50±√(50^2 - 4(1.862)(-202)))/(2*1.862) = (50±√4004.496)/3.722 = (50±63.281)/3.722 = -3.566 or 30.419
*March 26, 2015*

**math**

the dimensions are x,y,3
*March 26, 2015*

**Math**

false 6x1 You can only multiply two matrices if the columns of the 1st are the same as the rows of the second. That is, the dimensions must be of the form axb and bxc a and c may be anything, but the b's must match. The result is axc.
*March 26, 2015*

**Math**

just solve 2^(-t/1590) = 1/5 since 2^-2 = 1/4, you should expect an answer something more than two half-lives.
*March 26, 2015*

**Math question**

33+55-14 = 74 students liked something That means 26 liked nothing So, the number not liking orange is 26+(76-33) = 69 How did you arrive at 67? As usual, check my math
*March 26, 2015*

**math**

(1060-560)/1060 * 100 = 47%
*March 26, 2015*

**Calculus 2 (Differential Equation)**

If we pick a different c, the solution looks a little more symmetric, and more like the original equation: y = sin(arcsin(x)+arcsin(c)) y = sin(arcsin(x))cos(arcsin(c)) + cos(arcsin(x))sin(arcsin(c)) = x√(1-c^2) + c√(1-x^2) Just a thought. A bit ugly because c ...
*March 26, 2015*

**Math**

2m = 200 cm so, subtract the 15, and what do you have left?
*March 26, 2015*

**Physics**

since 1A = 1C/s, you have a current of 1C/.09s = 11.11 amps now just recall your formulas for power and energy
*March 25, 2015*

**Math if my answer is correct**

I get -0.04 and 26.89 what did you do to get your answers?
*March 25, 2015*

**Math**

That's what I get
*March 25, 2015*

**algebra**

It can indeed be either, depending on whether you are given a set of six letters, or allowed to choose your own six from the whole alphabet.
*March 25, 2015*

**physics**

how long does it take to fall? 4.9t^2 = 310 so, its downward speed is v = 9.8t
*March 25, 2015*

**algebra**

y >= 4x-5 For inequalities, the solution is a whole set of numbers, not just one. Plot the line y = 4x-5 Your inequality as as its solution everywhere in the whole x-y plane which is above that line, since that is where y is greater than the values lying on the line. The ...
*March 25, 2015*

**math**

since 72° is 1/5 of 360°, 3 slices is 1/5 of the pie. That help? The real question is, how the heck do you cut a pie into an odd number of equal slices?
*March 25, 2015*

**physics**

F = ma what's the trouble? Forget your Pythagorean Theorem?
*March 25, 2015*

**math**

since the concentrate is 100% juice, and the water is 0% juice, we have 100x + 0(12-x) = 15(12) x = 1.8
*March 25, 2015*

**math**

.36x + .50y = .37(100) Your language should read One equation in a system for solving this problem is x+y=100. What is the other equation? Since you gave no choices...
*March 25, 2015*

**algebra**

man! what a lot of words! Why not just list the points on the graph? (4,-4),(3,-3),(5,-3) Right there we see the vertex is at (4,-4), so y = a(x-4)^2 - 4 Now we have points (1,5),(7,5) 5 = a(-3)^2 - 4 = 9a-4 a = 1 so, y = (x-4)^2 - 4
*March 25, 2015*

**Math**

x/2 - 1 = (x-1)/3 x = 4 half of 4 is 2 yellows to start with less 1, leaves 1 yellow of 3 birds left
*March 25, 2015*

**math urgent**

recall the projection of b on a: p_a(b) = a.b * a/(a.a) v1 = u1 = (1,2,0) v2 = u2 - p_v1(u2) = (1,0,0) - (1/5,2/5,0) = (4/5,-2/5,0) v3 = u3 - p(u3,v1) - p(u3,v2) = (1,0,1) - (1/5,2/5,0) - (4/5,-2/5,0) = (0,0,1) check: v1.v2 = 4/5 - 4/5 = 0 v1.v3 = 0 v2.v3 = 0 so, v1,v2,v3 are ...
*March 25, 2015*

**Calc**

If y is the number of rebates, then the revenue is r(y) = (420-16y)(1300+160y) assuming only enough sets are made to sell out, then x = 1300+160y so, the profit is revenue less cost p(y) = r(y) - c(1300+160y) = (420-16y)(1300+160y) - (91000+140(1300+160y)) = -2560y^2 + 24000y...
*March 25, 2015*

**Math/Science**

there are 1000 micros per milli so, 10mm = 10,000 µm Since 1m = 1000mm, 10mm = 0.01m You did your conversion just backwards.
*March 25, 2015*

**Math**

??? if 4.8 ml must be added, I'd say the volume is 4.8 ml What am I missing? or, How has the question been garbled? Maybe you should clarify just what the named volumes comprise.
*March 25, 2015*

**math**

Unless we know how many students belong to more than one of the groups, there is no way to know how many total students were sampled. So, any or none of the choices could be correct.
*March 25, 2015*

**Math**

A (or any of the answers!) is correct only if there are exactly 100 stamps in all. All we are told is that there are 5% more from Norway than from France. If there are 1000 stamps, then there are 50 more, not 5.
*March 25, 2015*

**math - question stuck!**

if x is the combined mass of truck and wheat, and b is the # bushels, then b-300 = (500-300)/(21.6-16.2) (x-16.2) b = 37.037x - 300 so, find x when b=600 Now, if the truck weighs t and each bushel of wheat weighs w, we have t + 300w = 16.2 t + 500w = 21.6 so, w = 0.027, and t...
*March 25, 2015*

**Comprehensive Science**

You are correct.
*March 25, 2015*

**Alg. 2**

just plug in the numbers, assuming p(t) = ae^kt p(0) = 35000, so a = 35000 p(15) = 35000 e^15k = 21000, so k = -0.034 p(t) = 35000 e^-.034t e^-.034 = 0.9665, so the population is decreasing by 3.35% per year
*March 25, 2015*

**math proportions**

1 1/6 is 1/3 of 3 1/2 so, to do the job in 1/3 the time, we need 3 times the editors, or 15 Or, since the amount of work is constant, (3 1/2)(5) = (1 1/6)(x) x = 15
*March 25, 2015*

**Math**

in feet, the dirt is (9)(16)(1/3) = 48 ft^3 so, just divide that by 27 and multiply by the cost per cubic yard of dirt.
*March 25, 2015*

**math**

You just gave an example. Go ask 20 visitors their age. That's probably not a good example, since it's fairly hard to pick truly random people. But, you might count the number of people entering or leaving in a certain time period, and tracking that value over the ...
*March 25, 2015*

**Algebra (Math)**

these are just vertical or horizontal lines. clearly, the first set of equations intersect at (2,-3) The second intersect where y=2 so, plugging that into the second equation, x+2*2=10 x = 6 and they intersect at (6,2) Having said that, and solved the systems, go ahead and ...
*March 25, 2015*

**Math**

note that each gallon of cleaning solution treats 8 pails of water. So, now how many pails, to use up 16 gallons of solution?
*March 25, 2015*

**Pre-Calculus**

(s+6)^2 = 3/4 s+6 = ±√3/2 s = -6±√3/2 This is where it helps to keep track of things s = -6 ± (√3/2) NOT s = (-6±√3)/2 so, putting it all over 2, s = (-12±√3)/2
*March 25, 2015*

**math**

take a look at the number line. 29035 is to the right of 0. -1349 is to the left of 0. so, the distance between them (the difference, in other words) is 29035 - (-1349) = 29035+1349 = 30384
*March 25, 2015*

**Algebra**

that's only about 6.5 meters on a side. So, probably not elephants, nor mice. What smallish animals do you know?
*March 25, 2015*

**math**

total change: 35 degrees total time: 7 hours so, average change is 35°/7hr = 5°/hr
*March 25, 2015*

**math**

you have difficulty adding and subtracting numbers?
*March 25, 2015*

**PreCalculus**

since the area of a circular segment is a = 1/2 r^2 (θ-sinθ) you need θ such that cos(θ/2) = x/8 so, you need to solve 1/2 * 64 (2*arccos(x/8)-sin(2*arccos(x/8))) = 64π/3 x = 2.12 inches ---------------------------------- 3.5 mi/hr = 0.058 mi/min If ...
*March 24, 2015*

**math**

42 feet
*March 24, 2015*

**math**

If the 2nd piece is x, then x+3.57 + x + x+2.97 = 15
*March 24, 2015*

**geometry**

c = 2πr, so r = C/2π v = 4/3 π r^3 = 4/3 π (C/2π)^3 = 4/3 π C^3/8π^3 = 1/6 C^3/π^2
*March 24, 2015*

**math**

how about a 7-layer pyramid, with each layer 1 block wider than the layer above? Start with just 1 block on top.
*March 24, 2015*

**math**

x+y = 90
*March 24, 2015*

**geometry**

it's a frustrum of a cone.
*March 24, 2015*

**Solid Mensuration**

recall the volume of a spherical cap, as found here: http://en.wikipedia.org/wiki/Spherical_cap Now just plug in your numbers.
*March 24, 2015*

**Solid mensuration**

just look up the formula for the volume of a spherical cap of radius r and height h. Then plug in your numbers. Hint: find the volume of the smaller cap and subtract it from the whole ball. See here: http://en.wikipedia.org/wiki/Spherical_cap
*March 24, 2015*

**math**

recall that BC-AB < AC < BC+AB
*March 24, 2015*

**PHYSICS -urgent**

horizontal is constant at 92 m/s vertical is 9.8*19.9 so, (d) is just the resultant speed s, where s^2 = h^2 + v^2
*March 24, 2015*

**Implicit Differentiation (Please HELP)**

x^2 - 4y^2 + 1292 = 0 2x - 8yy' = 0 y' = x/4y You have x and y, so y' = 1/4 the line is thus y-8 = 1/4 (x-8) see at http://www.wolframalpha.com/input/?i=plot+x%5E2+%E2%88%92+4y%5E2+%2B+192+%3D+0%2C+y+%3D+1%2F4+%28x-8%29%2B8
*March 24, 2015*

**algebra**

√18/(√18-3) recall that (a-b)(a+b) = a^2-b^2. So, multiply by the "conjugate" to get √18(√18+3) / (√18-3)(√18+3) = (18+3√18)/(18-9) = (18+3√18)/9 = (6+√18)/3 = 3+√2 (4-3√2)^2 = 4^2 - 2(4)(3√2...
*March 24, 2015*

**Math**

any two points can be joined by a single line. In this case it's y-52488 = ((-393216-52488)/(-4-3))(x-3) There are many power functions which can go through any two points.
*March 24, 2015*

**math**

which is greater 8/4 or 5/3? and what do you mean by "over" when talking about paints?
*March 24, 2015*

**Math**

original size: w(w+2) after folding, the box is (w-12)(w+2-12)6 = 4050 w = 37 so, the original piece was 37x39
*March 24, 2015*

**Math Check**

How about -10x + 2y = 48 -5x - 3/2 y = -9 or, even better, -5x + y = 24 -10x - 3y = -18 or, getting rid of all the useless minus signs, 5x - y = -24 10x + 3y = 18
*March 24, 2015*

**math**

so, no effort on your part, eh?
*March 24, 2015*

**math**

a(x) domain: same as that of f range: [0,225) since (-15,2] = (-15,0]U[0,2] square those and you have [0,225)U[0,4] What do you get for b & c?
*March 24, 2015*

**Math Help!!!**

That's better.
*March 24, 2015*

**Math Help!!!**

#4: try again the others look good.
*March 24, 2015*

**Math**

Start with the whole amount, then subtract what was used. The result is what was left: 1 - 1/4 - x = 3/8 x = 3/8 for the cookies why did you use 3/8 - 1/4? 3/8 is how much she had left, and 1/4 was for the cake. How does that tell you anything about the cookies?
*March 24, 2015*

**Math**

Looks more like A to me. You noted the constant ratio, but that is a mark of a GP, not an AP. If you truly have no idea, you clearly need to review what it means to be a geometric or arithmetic sequence. It's annoying when someone comes asking for help, saying that they ...
*March 24, 2015*

**Math, Algebra**

You did not come up with an equation. You have an expression, and it does not provide a value for x. d = s + 3/8 s = f - 3/8 so, d = f - 3/8 + 3/8 = f the dog weighs the same as the ferret, or 1/2 lb must all be babies, eh? Or maybe small plush toys.
*March 24, 2015*

**Math**

well, 987*7 = 6909 = 11*628 + 1 not sure what you mean by inverse, but x=7 is a solution to the equation.
*March 24, 2015*

**Physics**

2.2 m/s is an angular speed of 2.2/35π = 0.02 rad/s so, its angular acceleration is (.02rad/s)/(15s) = 0.00133 rad/s^2 I expect you can find the other one.
*March 24, 2015*

**maths**

dice is already plural. No such word as dices. well, the chance of any one die's being even or odd is 1/2 So, the chance of all three being even or all odd is (1/2)^3, since the events are independent.
*March 24, 2015*

**math**

if x of 2%, then the rest (120-x) is 21%. So, .02x + .21(120-x) = .07*120
*March 24, 2015*