Sunday

February 14, 2016
Total # Posts: 37,657

**Math**

not differentiable if f'(x) is undefined. f'(x) = 1/√(1-x^2) so f' is undefined at x=±1 Now review the principal values of arcsin(x) cusps and corners are not differentiable, since the limit of f' is not the same from both sides.
*January 11, 2016*

**math**

since each triangle has sides 1/2 as big, the areas are 1/4 as big. So, just form a G.P. of the desired quantities and work with that.
*January 11, 2016*

**Math**

a+c = 9 8a+5c = 54
*January 11, 2016*

**Math**

Assuming you mean (5m^6)/(3n) that is just 5/3 m^6/n If the n is a typo, then you have 5/3 m^5
*January 11, 2016*

**math - eh?**

no idea what you're asking. Care to elaborate a bit?
*January 11, 2016*

**Math**

if you want 12, buy 10. If you want 26, buy 20 and that gives you 24, so then 2 more.
*January 11, 2016*

**MATHS**

just use the power rule and integrate each term separately. recall that ∫x^n dx = 1/(n+1) x^(n+1)
*January 11, 2016*

**math**

4n-3 <= 21
*January 11, 2016*

**Math (Help) thx!**

negative exponents move values from numerator to denominator and vice-versa. 7^-2 = 1/7^2 = 1/49
*January 11, 2016*

**Math**

(n+4)+n(n+2)+n=0 (n+4)+n(n+2+1)=0 (n+4)+n(n+3) = 0 n+4+n^2+3n = 0 n^2+4n+4 = 0 (n+2)^2 = 0 n = -2 or, n+2+2 + n(n+2) + n = 0 (n+2)+n(n+2) + n+2 = 0 2(n+2)+n(n+2) = 0 (n+2)(n+2) = 0 (n+2)^2 = 0
*January 11, 2016*

**Math log equation**

5^2x = (5^x)^2 So, make things easier to look at by letting u = 5^x Then you have u^2+20u-125 = 0 (u+25)(u-5) = 0 u = -25 or 5 But, 5^x is never negative, so we end up with u=5 5^x = 5 x = 1 check: 5^2 + 20*5 -125 = 25+100-125 = 0
*January 11, 2016*

**Math**

selling price will be 450000*1.03^10 Then just subtract the initial cost to get the profit.
*January 11, 2016*

**Math**

6 - (-2) C'mon, read your text.
*January 11, 2016*

**Math**

since the slope is constant, you need (n-4)/(6+2) = (4-1)/(-2-1) Now you can find n. Or, thinking about it another way, y increased by 3 when x decreased by 3. So, y will decrease by 8 if x increases by 8.
*January 11, 2016*

**Math log help**

Geez - give it a break, willya? Check your previous posts and be willing to wait a bit...
*January 11, 2016*

**Math**

Been there, done that http://www.jiskha.com/display.cgi?id=1452547715
*January 11, 2016*

**Math**

Not very patient, are ya? http://www.jiskha.com/display.cgi?id=1452547612
*January 11, 2016*

**Math logs**

Assuming the usual sloppiness with parentheses, we have 10^(3x-8) = 2^(5-x) (3x-8)log10 = (5-x)log2 (3log10)x - 8log10 = 5log2 - (log2)x x(log1000+log2) = 5log2+8log10 xlog2000 = log(32*10^8) x = log(32*10^8)/log(2000) x ≈ 2.88 Or, working a different way, 10^(3x-8) = 2...
*January 11, 2016*

**Algebra logs please help**

since 9 = 3^2, log3(n) = 2log9(n) That is, the power of 3 needed for a number is twice as big as the power of 9. So, we have 2log9(x) = log9(6x) log9(x^2) = log9(6x) x^2 = 6x x = 0 or 6 0 not allowed, so x=6
*January 11, 2016*

**Math**

#1 a 4x4 grid has 16 blocks Care to change your answer? #2 32% = 32/100 = 8/25 Care to change your answer? #3 6/24 = 1/4 Care to change your answer? #4 .09 = 9/100 Care to change your answer? #5 ok #6 4/9 = 0.44444... 11/25 = 44/100 That should clear things up #7 ok #8 9/15 = ...
*January 11, 2016*

**Math @angie**

your answer was easy to come by, but it did not answer the question. Also, 2/3 + 1/2 is NOT 3/5 Better review your fractions some before answering questions on them.
*January 11, 2016*

**Math**

correct. good job.
*January 11, 2016*

**Math**

did you actually try x=-6 to see whether you get the same y for both equations?
*January 11, 2016*

**Math**

well, if x=20, then y=70, since they add to 90. does 20 = 2*70-30? what did you do first?
*January 11, 2016*

**algebra**

15.99x <= 59.95
*January 11, 2016*

**@Studier2004**

42/6 is indeed 7, but it is not the answer to the question.
*January 11, 2016*

**math**

If the length is L, then 2(w+L) = 42 2(6+L) = 42 ...
*January 11, 2016*

**Math**

correct on all three.
*January 11, 2016*

**MATH HELP**

don't see any gold stars. You want to just write the question number, followed by your answers?
*January 11, 2016*

**Math**

correct.
*January 11, 2016*

**Math**

Hmmm. does 34 = 32?
*January 11, 2016*

**Math**

multiply the top one by 2, and you have 3x+4y=22 3x+6y=22 Now what do you think?
*January 11, 2016*

**Math**

whatever you do to one side, you must also do to the other side, if they are to remain equal. You subtracted x in your first step, but only on the left. If you had tried a value for x and y, you would have seen that your solution was wrong. y = -x+7, so let x=1, and y is -6. ...
*January 11, 2016*

**algebra 1**

multiply the 2nd equation by 5 and you have 3x-5y = 21 10x+5y = 5 Now you can eliminate y and get x, then figure y.
*January 11, 2016*

**Math**

The water level rose 2 cm. So, the volume of the stones is 2*20*15=600 cm^3 This assumes that the stones were completely covered by water.
*January 11, 2016*

**Math- steve? reiny?**

Does f^-1(x) even exist? f'(x) = 5x^4+6x^2+1 That is always positive, which means that the graph of f(x) does not change direction, so it passes the horizontal-line test. where is f(x) = 3? x^5+2x^3+x-1 = 3 x^5+2x^3+x-4 = 0 a little synthetic division shows that x=1 is a ...
*January 11, 2016*

**Math**

divide into 5 equal parts. Then use 1 part and 4 parts for the lengths.
*January 11, 2016*

**Algebra**

s = 3d m+1 = 6d m+10 = 14+(s+10)+(d+10) solve to find m. I get non-integer values for s and d. If "three times older" means d+3d=4d, then I get integer values, but the man is 149. Not likely.
*January 10, 2016*

**Algebra (Quadratic)**

If the width is w, the length must be 50-w. So, the area is a = w(50-w) The maximum area is achieved when x=25. You can find what it is. Note that the max area is when the rectangle is a square.
*January 10, 2016*

**maths**

If you mean 6x^2-x+3 < 5x^2+5x-5 then just collect terms on one side, and you get x^2-6x+8 < 0 (x-2)(x-4) < 0 This is a parabola which opens upward, so it is negative between the roots. Thus 2 < x < 4 A product is negative if exactly one of the factors is negative.
*January 10, 2016*

**Mathematics**

If you are using A for θ, then clearly θ=π/4 is a straight line with slope 1, so that is just y = x r = a sin2θ r = 2a sinθ cosθ r^3 = 2a rsinθ rcosθ (x^2+y^2)^(3/2) = axy But that only gives half of the graph, where xy is positive.
*January 10, 2016*

**Calculus**

surely you jest! The critical points are where f' = 0. f'(x) = -3sin3x You know that sin(u)=0 when u is a multiple of pi. So, f'(x) = 0 when 3x is a multiple of pi: x= 0, pi/3, 2pi/3, ...
*January 10, 2016*

**Trig - 9th grade**

this doesn't look easy. I'd attack it like this: 10sinx cosx + 3sinx - 1 = 0 sinx(10cosx+3) = 1 sinx = 1/(10cosx+3) sin^2x = 1/(100cos^2x + 60cosx + 9) (1-cos^2x)(100cos^2x+60cosx+9) - 1 = 0 Expand that out, and you have a 4th-degree polynomial in cosx. Guaranteed not ...
*January 10, 2016*

**maths**

we see that both pipes together can fill the the tank in 120/7 minutes: 1/t = 1/40 + 1/30 t = 7/120 So, after 5 minutes, they have filled 35/120 = 7/24 of the tank. So, it will take A 7/24*40 = 35/3 minutes to fill the rest. Total time: 5 + 35/3 = 16 2/3 minutes.
*January 10, 2016*

**Calculus**

while f" = 1/x, f is not defined for x<=0. So, f is concave up for all x>0. f = 2^(x/2) f' = ln2/2 2^(x/2) f" = (ln2/2)^2 2^(x/2) This is just e^kx in disguise. It is concave up everywhere. There are no critical points. f' = x√(9-x^2) f'=0 at ...
*January 10, 2016*

**Math**

If the calorie content of the pies are p and h, respectively, then we have (1/2)p + (3/4)h = 765 (1/4)p + h = 745 Now just solve for p and h. It might be less cumbersome to clear the fractions: 2p + 3h = 3060 p + 4h = 2980
*January 10, 2016*

**Algebra**

OHH! Thank you very much, that would have been a pretty frustrating error if I continued without noticing! Thank you, Damon. Have a great night!
*January 9, 2016*

**Algebra**

so it would then turn into 9y+12y+15y-45=243 36y-45=243 ( add the y's together) 36y = 288 (add 45 to 243) y = 8? (288 divided by 36)
*January 9, 2016*

**Algebra**

If someone could just show me how to set up a formula that would be great!
*January 9, 2016*

**Algebra**

A stamp collection consists of 3¢, 12¢, and 15¢ stamps. The number of 3¢ stamps is three times the number of 12¢ stamps. The number of 15¢ stamps is three less than the number of 12¢ stamps. The total value of the stamps in the collection is...
*January 9, 2016*

**Geometry**

hard to say, without knowing T,U,V
*January 9, 2016*

**MATH Precalculus**

Draw a diagram! clearly, if f(t) is the distance in feet, for 0<=t<=6, f(t) = 15t for 6<=t<=12, f(t) = √(90^2+(15t)^2)
*January 9, 2016*

**geometry**

s = rθ = r(2π/12) = π/6 r
*January 9, 2016*

**math**

You know from eq #2 that y=x+4. So, plug that into eq #1 and you have x + 4(x+4) = 1 Now you can find x.
*January 9, 2016*

**Math**

the surface area is 2πr^2 + 2πrh = 2π(r^2+hr) Now it's clear that r^2+hr=16... Now, using h=r+4, you have 2πr(r+r+4) = 32π
*January 9, 2016*

**physics**

the circumference is 4π. SO, the angular velocity is 16m/s * 1rev/4πm * 2πrad/rev = 32π/4π = 8 rad/s
*January 9, 2016*

**Direct variation algebra 2**

since V = kG, V/G=k, a constant. So, you want to find V such that V/11 = 36/4
*January 9, 2016*

**math**

What GP's are possible? If the 3 numbers are chosen independently, then we have 1,1,1 1,2,4 1,3,9 1,4,16 1,5,25 1,6,36 1,7,49 2,2,2 2,4,8 2,6,18 2,8,32 2,10,50 3,3,3 3,6,12 3,9,27 3,12,48 4,4,4 4,8,16 4,12,36 5,5,5 5,10,20 5,15,45 6,6,6 6,12,24 and so on. If the three ...
*January 9, 2016*

**math**

area of a circle is pi r^2 So, how far could the bear have walked in 4 hours? 4*2=8. use that for the radius. Then use 5*2 for the radius in the 2nd part, then subtract.
*January 8, 2016*

**Calculus @ Henry**

I worked some on this earlier, and botched it a bit, so here goes again. A water tank is made by rotating f(x)=2^x-1 between [0,2] about the y-axis. The water tank is initially full, when a hole is opened at the bottom tip so that the water drains at a rate of 4 unit^3/second...
*January 8, 2016*

**Geometry**

The first problem is discussed here: http://www.algebra.com/algebra/homework/Triangles/The-line-segment-joining-the-midpoints-of-two-sides-of-a-triangle.lesson Google is your friend. Most problems posted here have been discussed many times on the web. For #2, if you draw a ...
*January 8, 2016*

**Algebra**

The sum of two numbers is fourteen. Using x to represent the larger of the two numbers, translate "the difference between five more than the larger number and three times the smaller number" into a variable expression. Then simplify.
*January 8, 2016*

**Calculus**

hint: since a = s^2, da = 2s ds
*January 8, 2016*

**apex geometry**

too many typos to proceed. No diagram, but then none needed, since all circles are similar.
*January 8, 2016*

**maths**

x+19 = 48 x = 48-19 ...
*January 8, 2016*

**calculus**

If the radius of the circle is x, the side of the triangle is y, and the side of the square is z, then we have 2πx+3y+4z = 1 a = πx^2 + √3/4 y^2 + z^2 da/dx = 2πx da/dy = √3/2 y = √3/2 (1-2πx-4z) da/dz = 2z a will have a maximum where all ...
*January 8, 2016*

**maths**

At any point (x, 3/2 x) on the line, the distance from the origin is d^2 = x^2 + 9/4 x^2 = 13/4 x^2 If the circle's center is at (h,3h/2), then, we have (x-h)^2 + (y-(3h/2))^2 = 13/4 h^2 (5/2-h)^2 + (1/2-(3h/2))^2 = 13/4 h^2 h=1 So, the circle is (x-1)^2 + (y-3/2)^2 = 13/4...
*January 8, 2016*

**calc**

what's with all the words? s(t) = -t^3/3 + 13t^2/2 - 30t when the particle is mofing to the right, s(t) is increasing, so ds/dt > 0 -t^2 + 13t - 30 > 0 3 < t < 10 Since our domain is 0<t<9, our interval is thus 3<t<9
*January 8, 2016*

**maths**

2s^2 = 98 s = 7
*January 8, 2016*

**Calculus**

When the height of the water is y, then the radius of the surface is x=log_2(y+1) Thus, the volume of the water when the depth is h is ∫[0,h] πx^2 dy Now, ∫π(log_2(y+1))^2 dy = π(y+1)(ln^2(y+1)-2ln(y+1)+2)/ln^2(2) That gives me ∫[0,3]π(...
*January 8, 2016*

**Geometry**

since consecutive angles add to 180, we have 8x+1 + 12x+19 = 180 Now find x, and then the angle measure.
*January 7, 2016*

**Geometry**

Assume the following is a true statement. If it is raining, I will carry an umbrella. Which form of the original statement must also be true? a- converse b-- inverse c- contrapositive d- biconditional My answer is c contrapositive
*January 7, 2016*

**Math**

#1. The geese eat m, 2m-1, 4m-3, 8m-7, 16m-15, 32m-21 Sum: 63m-47 Typo in answers? #2. T - (T/2-6) - (T/3-2) = T/6 + 8 #3. 3x(x+4) if x=3, that's 63 #4. -3^2 + 24/2*3 + 6*2 + 3^0 = -9 + 36 + 12 + 1 = 40 Maybe this will help
*January 7, 2016*

**Algebra @Damon**

eh?
*January 7, 2016*

**Algebra**

The number of hours, h <= 4 So, the charges c <= 85*8 + 50
*January 7, 2016*

**math geometry**

Heck, just draw the line AB. Then pick a point X close to the line and Y far away from the line. While XY is the pb of AB, AB is not necessarily the pb of XY.
*January 7, 2016*

**Math**

The Pythagorean Theorem tells you that the exact length of lighting is √(8^2+14^2) = 16.12 feet So, now, what's the answer you need?
*January 7, 2016*

**MATH**

no idea what you're after. Permuting 5 numbers will not ever produce a sixth number.
*January 7, 2016*

**Math**

compare A:12.00*5 vs B:0.08*125*5 As you see, the 5-day period is useless. The better deal for 1 day is the better deal for any number of days, if the same number of minutes is used.
*January 7, 2016*

**Mathematics**

4π/3 x^3 = 2100 x^3 = 1575/π a = 4πx^2 = ? 2π/3 r^3 = 2π/3*15^3 = 2250π for the cylinder, then πr^2 45/2 = 2250π r = 10
*January 7, 2016*

**Math**

using the remainder theorem, f(a) is the remainder when dividing by (x-a), we have f(1) = 0 f(-1) = 2 f(2) = 6 So, now you have three equations to use: a+b+c = 0 a-b+c = 2 4a+2b+c = 6 7/3 x^2 - x - 4/3 check it to be sure.
*January 7, 2016*

**Math**

Hmm. Seems pretty clear to me. When you bring up the page, there are various buttons. One of them is labeled between. Enter your two Z values, and it will show the area. Play around there for a while, and it will become clear how it all fits together. You can enter Z vales, or...
*January 7, 2016*

**Math**

3D is correct. #4 is misleading, since it appears that the 1st two terms are 3 and 888. Lose the comma and things are clearer. There is a common ratio of 1/18, so B
*January 7, 2016*

**Math**

They look good to me.
*January 7, 2016*

**Precalculus**

or, just draw the triangle and label the sides. The missing side is √(49-9) = √40 Then you can read off all the trig functions just by looking at the sides and using the proper ones.
*January 7, 2016*

**maths**

clearly the sphere has diameter 14. So, just subtract to get the wasted metal: 14^2 * 20 - 4π/3 * 7^3
*January 7, 2016*

**math**

assuming they both show the correct time now, then since the fast clock gains 8 minutes per hour, it will gain an hour every 7.5 hours, and the minute hands will be aligned. It will gain 2 hours in 15 hours. Thus, after 6*15=90 hours, it will have gained 12 hours, and the ...
*January 7, 2016*

**Maths**

(2x+1)(x-1)
*January 7, 2016*

**math**

the volume of the metal is π(5^2 - 4^2)(35) cm^3 Now you can find the weight.
*January 7, 2016*

**math**

(m-5) = (s-5)^2 m+10 = 2(s+10) Now you can find m and s. You will get two answers, but only one is possible, given the conditions above.
*January 7, 2016*

**Math**

10/2 (2a+9d) = 220 Now, the odd terms are a, a+2d, a+4d, ... So they form a 5-term AP whose common difference is 2d, and whose sum is 5/2 (2a+4(2d)) = 100 Now you can find a and d.
*January 7, 2016*

**math**

The ellipse is degenerate, since the foci are at the vertices.
*January 7, 2016*

**Math**

with a 50% markup, the selling price is 1.50 times the cost. So, the cost is 200.
*January 7, 2016*

**Math**

the slope of the line through the two points is 5/-10 = -1/2. So, what is the line through the origin with that slope?
*January 7, 2016*

**Math**

clearly the line is y = 4/3 x - 5 So, just rearrange that to the general form ax+by+c = 0
*January 7, 2016*

**Math**

P=kQR, so P/QR is constant. Thus, you want P where P/2 = 420/21
*January 7, 2016*

**Math**

Inverse variation means that yz = k, a constant. No matter which values you have, their product stays the same. So, you want to find z such that 4*25 = 10z
*January 7, 2016*

**Math**

2/5 + 1/4 = 13/20 hr * 60 min/hr = 39 min
*January 7, 2016*

**math**

it is the distance between the two opposite vertices. Just use your distance formula.
*January 6, 2016*

**Math**

If the current speed is c, then the boat's speed is 5c. Since time = distance/speed, 48/(5c-c) + 48/(5c+c) = 5 12/c + 8/c = 5 ...
*January 6, 2016*