Thursday

November 26, 2015
Total # Posts: 35,801

**Math**

If the tire has width w, then the inner radius is 2w, and the entire area has radius 3w. So, π(9w^2-4w^2)/π(9w^2) = 5/9 = .5555 or 56%
*October 10, 2015*

**MATH**

Not quite... The cost C is C = 8(2W+L)+15L since LW=400, = 8(2(400/L)+L) + 15L = 8(800/L + L) + 15L = 6400/L + 23L
*October 10, 2015*

**Calculus**

Looks like A&B to me. I mean, have you tried actually drawing a vector xi+yj, with its tail at (x,y)?
*October 10, 2015*

**Calculus**

using implicit differentiation, 2(x^2+y^2)(2x+2yy') = 16y' x(x^2+y^2) + y(x^2+y^2)y' - 4y' = 0 y' = -x(x^2+y^2)/(x^2y + y^3 - 4) So, the slope is vertical where x^2y-y^3 -4 = 0 y(x^2-y^2) = 4 Not easy to solve in general, but a little playing around gives x...
*October 10, 2015*

**Physics i need hlp i have exams next weeks that is why i post the question that which i cannot do**

c = av + b/v cv = av^2 + b av^2 - cv + b = 0 now just use the quadratic formula to find v. There will only be a maximum cost if a<0, since then the parabola will open downward.
*October 10, 2015*

**Geometery i need help**

well, let's assume the octagon is just a regular polygon. It consists of eight isosceles triangles, each with two sides of 12, and a vertex angle of θ=45°. So, if the base of each triangle (one side of the octagon) is s, (s/2) = 12 sin(θ/2) Now just plug in ...
*October 10, 2015*

**Geometery i need help**

clearly the band forms an octagon (with rounded corners) with a diameter of 3 oranges, or 24mm. Now play around a bit with the dimensions of an octagon.
*October 10, 2015*

**trig**

so, cotθ = (√7)/2, meaning x = √7 y = 2 since cotθ = x/y
*October 10, 2015*

**trig**

recall that sinθ = y/r cosθ = x/r tanθ = y/x r^2 = x^2+y^2 So, in QIII, where x and y are both negative, tanθ = √5 = √5/1, so y = -√5 x = -1 r = √6 cotθ = x/y = 1/√5 secθ = r/x = -√6 For #1, do you mean (1/2) &#...
*October 10, 2015*

**maths**

clearly, the bonuses are (2/3 * 105), 105, (4/3 * 105) So, the total is 3*105 = 315
*October 10, 2015*

**Calculus**

You are correct. I fear that the answer choices relate to a different problem, since with a simple power, no logs will arise.
*October 10, 2015*

**How many of these number maths??**

(a) 7!/(3!2!) = 420 (b) If 3,4 are used, that leaves 5!/3! = 20 (c) divisible by 5 means that 3,4,5 are used, leaving 4!/3! = 6 (2) divisible by 2 means that 2,3,4 are used, leaving 4!/2! = 12
*October 10, 2015*

**precalculus**

better review your trig functions sinθ = x/r cosθ = y/r r^2 = x^2+y^2 You have a 3-4-5 triangle. Draw the dang thing! x = -3, so cosθ = -3/5
*October 10, 2015*

**precalculus**

in QII, x is negative, so cosθ = -3/5 The rest is easy, right?
*October 10, 2015*

**maths**

as usual, draw a diagram. The tower's height is 20 + 20 cot30° * tan60° = 20(1+tan^2 60°) = 20 sec^2 60° = 20 * 4 = 80
*October 10, 2015*

**geometry**

Just knowing the four sides of a quadrilateral does not help find the area. As you know, if you build such a figure, you can squash it around, because the joints are not rigid. Unless you know some of the angles or something, you cannot determine the area.
*October 10, 2015*

**MATH!**

D is the best bet. It appears not to repeat.
*October 10, 2015*

**Calculus i need help**

x^2 y + sin(xy) + y^4 x^2 + 3xy = 5 Just use the product rule and the chain rule: d/dx(x^2 y) = 2xy + x^2 y' d/dx(sin(xy)) = cos(xy) (y + xy') d/dx(x^2 y^4) = 2xy^4 + 4x^2y^3 y' d/dx(3xy) = 3y + 3xy') So, add them all up, collect the y' stuff, and it's ...
*October 10, 2015*

**Maths**

well, how long does it take to go 200 miles, if you travel 100 miles each hour?
*October 10, 2015*

**Pre-Calculus**

you must have some ideas about some of these topics. At the very least, use a graphing utility to see what the graph looks like, and most of the answers should become clear immediately.
*October 10, 2015*

**Grrr.**

Oops. I thought we were doing serious math homework here. My bad :-( Like 16/64 = 1/4 because you can just cancel the 6's.
*October 10, 2015*

**Prove also need help**

this is nonsense. Of course 13/12 is not 2 You want to fix up your question a bit?
*October 10, 2015*

**Trigonometry prove need help**

tan 45-b = (tan45-tanb)/(1+tan45 tanb) = (1-tanb)/(1+tanb) square that, and you have (1-2tanb+tan^2b)/(1+2tanb+tan^2b) = (sec^2b-2tanb)/(sec^2b+2tanb) = (1/cos^2b - 2sinb/cosb)(1/cos^2b + 2sinb/cosb) = (1-2sinb cosb)/(1+2sinb cosb) = (1-sin2b)/(1+sin2b) I think you have a typo...
*October 10, 2015*

**pre calc**

Tough to describe the function, when it not given...
*October 10, 2015*

**pre calc**

first, put the words into algebra. If there is x at 5.5% and y at 11%, you have: x+y <= 130000 x >= 40000 y <= 60000 maximize p = .055x + .11y Now just use your favorite linear programming tool.
*October 10, 2015*

**pre calc**

You've posted a bunch of these. Some have been done for you. No ideas yet?
*October 10, 2015*

**calculus**

that is the definition of an inverse function. For any f(x), f(f^-1(x)) = x f^-1(f(x)) = x if f is single-valued, which sinh(x) is. If you take sinh^-1 of both sides, you have sinh^-1(sinh(sinh^-1(x))) = sinh^-1(x) but that only helps if you already know that sinh^-1(sinh(u...
*October 10, 2015*

**Math**

for the short diagonal x, x^2 = 5^2+10^2-2*5*10 cos50° for the long diagonal y, y^2 = 5^2+10^2-2*5*10 cos130°
*October 10, 2015*

**calculus**

y' = (x^2-10x+16)/(x-5)^2 y" = 18/(x-5)^3 So, max/min if y'=0 max if y" < 0, min if y" > 0 The rest is just algebra.
*October 10, 2015*

**calculus**

Assuming the two walls meet at a right angle, x+y = 30 a = xy = x(30-x) this is just a parabola, with vertex at x=15. As usual, the area is a square. You can take the derivative if you want, but no calculus needed here...
*October 9, 2015*

**math**

just multiply both elements by the same nonzero value. Think of fractions.
*October 9, 2015*

**Maths**

why take the derivative to find t? It won't help here. Just expand and solve: 0.2t^3 - 2.84t^2 + 9.282t = 2.4 + 0.75t 0.2t^3 - 2.84t^2 + 8.532t - 2.4 = 0 Now you can fall back on graphical methods, or Newton's method or something you have in your bag of tricks.
*October 9, 2015*

**math**

sin = y/r cos = x/r tan = y/x r is always positive In QIV, x is positive and y is negative In QII, x is negative and y is positive So, in QII, cos,tan,cot,sec are negative in QIV, sin,tan,cot,csc are negative only tan,cot are negative in both.
*October 9, 2015*

**pre calc**

S1: 2 is a factor of 1^2+7*1 and so on. Clearly, since if n is odd, n^2 and 7n are both odd, so their sum is even if n is even. n^2 and 7n are both even, so their sum is even. Or, if n is odd (2k+1)^2+7(2k+1) = 4k^2+4k+1+14k+7 = 2(2k^2+9k+4) and similarly for even n=2k
*October 9, 2015*

**math**

4x+5y=10 2x+3y=8 x = -5 y = 6 Now just find 3x+4y
*October 9, 2015*

**Pre-calculus**

9^(2x-6)=6^(8x-5) (2x-6) log9 = (8x-5)log6 (2log9)x - 6log9 = (8log6)x - 5log6 x = (6log9 - 5log6)/(2log9 - 8log6) you can massage that a few ways, but that's the idea
*October 9, 2015*

**Math**

see http://www.jiskha.com/display.cgi?id=1444227515
*October 9, 2015*

**Trig**

after t seconds, Michael has gone 2t ft and Alyssa has gone 3t feet. So, the distance z between them using the law of cosines, is found using z^2 = (2t)^2 + (3t)^2 - 2(2t)(3t)cos60° so, plug in your time (in seconds!) and find z.
*October 9, 2015*

**precalc**

looks like our calculator agree!
*October 9, 2015*

**precalc**

Draw triangle LBM where the ball is at B; angle B is 158°. Using the law of sines, if the ball's distance from M is x, then x/sin9° = 23/sin158°
*October 9, 2015*

**Algebra**

(x+3)/(x+8)-(x-8)/(x-3) =[(x+3)(x-3) - (x-8)(x+8)]/[(x+8)(x-3)] =[(x^2-9)-(x^2-64)]/[(x+8)(x-3)] = (-9+64)/[(x+8)(x-3)] = 55/[(x+8)(x-3)] You probably forgot to use parentheses to keep track of quantities. But aside from that, what did you do with your denominator?
*October 9, 2015*

**geometry**

since DB bisects the angle ABC, the two smaller angles are equal. So, 12x+24 = 20x+16 So, find x, and you can figure the angles.
*October 9, 2015*

**MATH HELP PLEASE**

4718(1+.05/4)^(4n) = 5323 (1.0125)^(4n) = 1.1282 4n = log(1.1282)/log(1.0125) n = 2.4 or, roughly 2 1/2 years
*October 9, 2015*

**Math**

-2+5x-7=3x-9+2x collect constants and x's on each side: 5x-9 = 5x-9 Since both sides are the same, it will be true for any value of x at all!
*October 9, 2015*

**Calculus**

using shells, v = ∫[0,1] 2πrh dy where r = 1-y and h = √y - y^2 v = 2π∫[0,1] (1-y)(√y - y^2) dy = 11π/30 using washers, v = ∫[0,1] π(R^2-r^2) dx where R = 1-x^2 and r = 1-√x v = π∫[0,1] ((1-x^2)^2-(1-√x)^...
*October 9, 2015*

**Maths**

|a|-3/4=-5/8 |a| = -5/8 + 3/4 = 1/8 clearly, a = 1/8 or -1/8
*October 9, 2015*

**math**

As always, draw a diagram. The parabola has vertex at (1,0) and opens to the right. The line x=2 intersects the parabola at (2,1) and (2,-1). So, you will be revolving the sort-of-semicircular chink around the line y=-2, which is below the curve. So, as you say, v = ∫2&#...
*October 9, 2015*

**Maths**

|a|-3/4=-5/8 |a| = -5/8 + 3/4 = 1/8 clearly, a = 1/8 or -1/8
*October 9, 2015*

**Maths**

L1 has intercepts at A:(-6,0) and B:(0,4) L2 has gradient -3/2 and passes through (0,4), so L2 is y-4 = (-3/2)(x-0) 3x+2y-8 = 0 L2 passes through B:(0,4) and C:(8/3,0) So, if you plot the points, you can see that you have a triangle with base along the x-axis, and its third ...
*October 9, 2015*

**Maths**

why plug in 3 for x? Why change the polynomial? x^2 + 2kx - 3k = 0 the discriminant is (2k)^2 - 4(1)(-3k) = 4k^2 + 12k For two equal roots, the discriminant must be zero. 4k^2+12k = 4k(k+3) = 0 k = 0 or -3 k=0: clearly x^2=0 has two equal roots k = -3: x^2-6x+9 = (x-3)^2 has ...
*October 9, 2015*

**Algebra**

(8+12)/(4*5)=1
*October 9, 2015*

**Algebra**

24000(1+.0685/12)^(12*18) = 82,067.98
*October 9, 2015*

**math**

It's a little easier to check if you mark your answers with the questions. Saves a lot of scrolling back and forth. However, the wily teacher opens a 2nd window to avoid that, too! #1: 20/2 – 32 – (-2)2 = 10 - 32 - (-4) = 10 - 32 + 4 = -22+4 = -18 Since that'...
*October 9, 2015*

**Algebra**

in 2 hours, Molly was 54 miles ahead. Mark was going 18 mi/hr faster, so it took him 54/18 = 3 hours to catch up. But 3 is not the answer to the question ...
*October 9, 2015*

**Physics/trig**

as you recall, the equation of motion is y = tanθ x - g/(2(v cosθ)^2) x^2 So, plugging in your numbers, y = 0.664x - 0.00806x^2 That's a parabola with vertex at x=41.2
*October 9, 2015*

**pre calculus**

This is just a standard linear programming problem. For x breakfast packages and y afternoon packages, you want to maximize p=1.50x+2.00y subject to x/3 + y/2 <= 45 2x/3 + y/2 <= 70 Now just use your favorite linear programming tools.
*October 9, 2015*

**pre calculos**

Just substitute k for n and you have Sk. Same for k+1. Sk+1: 1∙2+2∙3+...+k(k+1)+(k+1)(k+2) = [(k+1)(k+2)(k+3)]/3 Can't get much simpler than that.
*October 9, 2015*

**math**

shift 3 left scale by 2 vertically reflect in x-axis In this case, the order does not really matter. Try them and see.
*October 9, 2015*

**prasanna high school**

been done. http://www.jiskha.com/display.cgi?id=1444216542
*October 9, 2015*

**math - eh?**

Not sure what you are saying here. When you say the building and the pole are at equal angles, do you mean the top of the building, or the bottom? The top of the pole, or the bottom?
*October 9, 2015*

**Maths**

-(x^2+3x)+7 3 = 2 * 3/2, so -(x^2 + 3x + 9/4) + 7 - 9/4 -(x + 3/2)^2 + 19/4
*October 9, 2015*

**Math**

Not to mention gazillions of others, like 99/100 87/150 1234124/2468247 and so on. I didn't see anything about having a single digit in the bottom or top.
*October 9, 2015*

**Math**

well, it has to double three time to be full, right?
*October 9, 2015*

**math**

well, 20 = 4*5 25 = 5*5 So, what do you think?
*October 9, 2015*

**Math**

not quite. 6 pizzas makes 48 slices 3 1/4 pizzas are 26 slices. So now, how many slices were left over? How would you interpret Janet's suggestion?
*October 9, 2015*

**pre calculus**

well, just plug in k and k+1 for n. You need to prove that if Sk is true, then Sk+1 is also true. Then, if you can show that S1 is true, then S2,S3,... are all true as well. 1+4+...+(3k-2)+(3(k+1)-2) = Sk+3(k+1)-2 = k(3k-1)/2 + 3(k+1)-2 = (k(3k-1) + 6(k+1)-4)/2 = (3k^2-k+6k+6-...
*October 8, 2015*

**math**

how much did each eat? Heck, they told you that. Convert each fraction to decimal to compare. 0.5 is 1/2. 2/3 = 0.666 and so on
*October 8, 2015*

**Math**

The one-digit factors of 54 are 1,2,3,6,9 so, which three of those add to 14?
*October 8, 2015*

**Science**

All the energy ultimately comes from the sun.
*October 8, 2015*

**trig**

nice formulas. Is there a question in there somewhere?
*October 8, 2015*

**math**

you want to add some parentheses, or at least some spaces, so we can work with that? As written, using the normal order of operations, you have 4-x^2/x^2+7x+12/2x-4/x+3 4-1+7x+6/x-4/x+3 3+7x+2/x+3 6 + 7x + 2/x I doubt that is what you had in mind.
*October 8, 2015*

**algebra**

enter your polynomials at http://calc101.com/webMathematica/long-divide.jsp and see all the details
*October 8, 2015*

**geometry**

assuming RST are collinear points, in that order, RS+ST=RT, so hmmm. If R bisects ST, and 5x=7 is a typo for 5x+7, then since SR=RT, 5x+7 = 15x-1 10x = 8 x = 4/5 But you may have had other things in mind. Remember, we cannot see what diagram you have in front of you. Nor can ...
*October 8, 2015*

**Pre Calculus**

(a) if you mean (3f+2g)(1) then that is 3f(1)+2g(1) = 3*50 + 2(-5) = 140 (f◦g)(-1) = f(g(-1)) = f(-3) = 10 f(x) = x^2 g(x) = x/(x+4) h(x) = g◦f = f/(f+4) = x^2/(x^2+4)
*October 8, 2015*

**math**

see related questions below
*October 8, 2015*

**math**

pick any five values for x. Multiply each by 18. Plot those points. Can you see what a useless exercise it is for you to ask us to plot a graph and verify it? Sheesh.
*October 8, 2015*

**Math**

one-digit factors of 54 are 1,2,3,6,9
*October 8, 2015*

**Math**

Let 2x be the least. Then the next 3 even integers are 2x+2, 2x+4, 2x+6 So, add them up: 2x + 2x+2 + 2x+4 + 2x+6 = 2x Now solve for x, and ... Extra credit: We used 2x to make sure it was an even number. What would have happened if we had just used x instead?
*October 8, 2015*

**Pre-Calc**

the same way you would simplify 2/3 + 3/2. Put it all over a common denominator: tan/(1+sec) + (1+sec)/tan = [tan^2 + (1+sec)^2]/(tan(1+sec)) = (tan^2 + 1+2sec+sec^2)/(tan(1+sec)) = (sec^2-1+1+2sec+sec^2)/(tan(1+sec)) = (2sec^2+2sec)/(tan(1+sec)) = 2sec(1+sec)/(tan(1+sec)) = ...
*October 8, 2015*

**Math Help**

oh, please...
*October 8, 2015*

**Math (Quadratics)**

You'll need to use the quadratic formula on that one. Or, completing the square, 8x^2+2x-4 = 0 8(x^2 + x/4) = 4 8(x^2 + x/4 + 1/64) = 4 + 8/64 8(x + 1/8)^2 = 4 + 1/8 (x + 1/8)^2 = 33/64 x + 1/8 = ±√33 / 8 x = -1/8 ±√33/8 x = (-1±√33)/8
*October 8, 2015*

**Algebra i need serious help**

Sorry, I only give jocose help. Since 3-x = -(x-3) |x-3| = |3-x| for all values of x
*October 8, 2015*

**Division need help urgently plz**

all you want is the last digit. So, look at the powers of 7: 7^1 = 7 7^2 = 49 7^3 ends in 3 7^4 ends in 1 since 3*7=21 913 = 4*228 + 1 So, 7^913 = 7^4^228 * 7 thus, it ends in 7
*October 8, 2015*

**Algebra 2**

try using ^ for powers. That is y^3 means y cubed. The formatting has messed things up to where they are incomprehensible.
*October 8, 2015*

**Physics**

220 km/hr = 2.20 * 10^5 m/hr So, there must be a headwind of 2.8-2.2 = 0.6 * 10^5 m/hr. That is, a wind blowing north at 60 km/hr
*October 8, 2015*

**Math**

paycheck: x food: 1/6 x, leaving 5/6 x house: 3/5 of 5/6 x = 1/2 x, leaving 1/3 x bills: 1/3 of 1/3 x = 1/9 x, leaving 2/9 x entertainment: 1/4 * 2/9 x = 1/18 x, leaving 1/6 x so, 150 = 1/6 x x = 900
*October 8, 2015*

**math please help!!**

the graph is concave down where 16e^-x^2 (2x^2-1) < 0 that is where 2x^2-1 < 0 x^2 < 1/2 so, f is concave down on the interval (-1/√2,1/√2)
*October 8, 2015*

**Math 125**

It appears that the number of calculators sold, as a function of the amount of discount (x) is p(x) = 10000+400x so, just plug in x=20 for the demand at $75.
*October 8, 2015*

**Calculus**

∫[0,8] 8x-x^2 dx = 4x^2 - 1/3 x^3 [0,8] = 4*8^2 - 1/3 * 8^3 = 256 - 512/3 = (768-512)/3 = 256/3 Maybe you should have shown your work.
*October 8, 2015*

**Mathematics(XI)**

google is your friend: https://answers.yahoo.com/question/index?qid=20121228030540AAIm82k
*October 8, 2015*

**math**

since √y = 7-x, √x + (7-x)^2 = 11 √x = -x^2+14x-38 x = x^4-28x^3+272x^2-1064x+1444 x^4-28x^3+272x^2-1065x+1444 = 0 (x-4)(x^3-24x^2+176x-361) = 0 good luck with the cubic. But, if x=4, y=9
*October 8, 2015*

**Find x algebra help**

no easy algebraic way to do this. However, with a little thought, you should be able to come up with 3^2-1 = 2^3
*October 8, 2015*

**Pre-Calculus**

well, just plug in the values: f(x)-f(1) = (-3x+2)-(-3*1+2) = -3x+3 Now divide by x-1 and you have (-3x+3)/(x-1) = -3(x-1)/(x-1) = -3 For the other, the same thing: f(x+∆x)-f(x) = 2(x+∆x)-2x = 2x+2∆x-2x = 2∆x Now divide by ∆x and you have 2∆...
*October 8, 2015*

**math**

a < b x >= y etc. If you have some specific questions, it would be a bit more useful to see how they can be answered.
*October 8, 2015*

**Algebra**

Looks like 9!-1 to me. Now, if you want (9!-6!)/(9-3)! that's 503. What is that supposed to model?
*October 8, 2015*

**Math**

If the faster person takes x hours, then the slower person takes (x+1) hours. So, how much of the job gets done in an hour? 1/x + 1/(x+1) = 1/5 Now just find x.
*October 8, 2015*

**Calculus 1**

the light turns through angle θ where dθ/dt = 4π. If the light hits x km away from P, then x = 4tanθ So, knowing that tanθ = 1/4, plug in the numbers and find dx/dt: dx/dt = 4 sec^2(θ) dθ/dt
*October 8, 2015*

**calculus**

I'll let you do the discussion. You just need to recall that f' = x^3 - 3x f" = 3x^2 - 3 f is increasing where f' > 0 f is concave up where f" > 0 f has max/min where f'=0 f has inflection where f" = 0
*October 8, 2015*

**Geometry**

as with the supplementary angles problem, 4x = (90-x)+10
*October 8, 2015*

**Geometry**

two angles are supplementary if they add to 180. So, if one angle is x, the other is (180-x), and you have 2x = (180-x)-36 2x = 133-x 3x = 144 x = 48
*October 8, 2015*