Tuesday

November 24, 2015
Total # Posts: 35,768

**Calculus - eh?**

As always, draw a diagram. Label the water works W. It sounds like C,W,D are in a straight line. If so, there is really very little calculus involved here. In fact, the least cost pipeline is to build it right at D. If C and D are x miles apart, and W is y miles from C, then ...
*October 15, 2015*

**maths**

f + (3f+2) = 102
*October 15, 2015*

**Science**

Since the only atoms involved are H2O, the gases are clearly hydrogen and oxygen. Since the water was changed into different compounds (in fact, elements), a chemical change took place. I expect you can check the boiling points of H2 and O2 to confirm the deduction.
*October 15, 2015*

**maths**

If the number is xy, then x+y=12 10x+y = 36+10y+x Now just find x and y. If that's too hard, just think of the pairs of digits that add to 12, and try them out.
*October 15, 2015*

**math**

If A takes x hours, and B takes x+6 hours, then we have 1/x + 1/(x+6) = 1/4 Now just find x, and then x+6.
*October 15, 2015*

**precal**

Pretty lousy account if it does not accrue interest. Anyway, just look up your formula for annuities, and plug in your numbers. Or check the related questions below. Or (gasp) give google a try.
*October 15, 2015*

**Math**

Assuming you meant (13-15x^2)/((x^2-1)(x+3)) then you get (1/2)/(x+1) - (1/4)/(x-1) - (61/4)/(x+3) If you mean x-3, then just make the fix. I trust you just wanted confirmation of your work, eh? If not, and you got stuck, how far did you get?
*October 15, 2015*

**Area of a triangle**

have you considered the angle bisector theorem, and the law of sines?
*October 15, 2015*

**Algebra 2**

come on, this is just Algebra I all over again. From the first equation, x = 17-2y Plug that into the 2nd equation and you have 17-2y-y=2 -3y=-15 y=5 Or, from the 2nd equation, x=y+2, so y+2+2y=17 3y=15 y=5 Or, just subtract the 2nd from the first, and you get 3y=15 y=5 In any...
*October 14, 2015*

**Algebra 2**

clearly, since you are given the slope and the y-intercept, the best representation is the slope-intercept form! y = 4x-6 You can massage that any way you like.
*October 14, 2015*

**Math🤓**

Assuming a rectangular field, total fence: 32+40+32+40 = 144 ft 144/4 = 36
*October 14, 2015*

**Maths**

w=3d (w-6)+(d-6) = 36 (3d-6)+(d-6) = 36 4d=48 d=12
*October 14, 2015*

**Math**

I like C, since there are 140/200 of the students with A or B blood.
*October 14, 2015*

**PreCalculus**

plug in your numbers: h(t) = -16t^2 + 4t + 10 Recall from your Algebra I that this is just a parabola, with vertex at x = -b/2a, or in this case, x = 1/8 h(1/8) = 41/4 This is no time to forget your earlier math!
*October 14, 2015*

**Calculus**

Using the Pythagorean Theorem from your Algebra I days, the distance to the plane, z, after the plane has gone x miles since being directly overhead, is z^2 = 2^2 + x^2 we want the rate at which the distance is changing, dz/dt. So, taking derivatives, and remembering the chain...
*October 14, 2015*

**Geometry**

since vertical angles are equal, and supplementary angles add to 180, if the vertical angles have measure x, then x+x = 180
*October 14, 2015*

**Math - PS**

My bad! 4 is not in the list. So, the sum is just zero.
*October 14, 2015*

**Math**

you want the sum of the integers from -3 to 4 they will be -3,-2,-1,0,1,2,3,4 Clearly the sum is just 4, since all the + and - pairs add to zero.
*October 14, 2015*

**Statistics**

for Z=-0.25, that is .25 std below the mean, or 62 - 0.25*12 = 62-3 = 59 Same for the others.
*October 14, 2015*

**maths**

mixed numbers are a pain. You have to convert them to fractions to do much with them. So, you have (83/12)÷(46/5)*(12/8) = (83/12)(5/46)(12/8) = (83*5*12)/(12*46*8) = 415/368 or 1 47/368
*October 14, 2015*

**MATH**

recall your 3-4-5 right triangle. Multiply each side by 0.7 and you choice (A). Or, you can just square all these numbers and see which two add up to the third in any given choice.
*October 14, 2015*

**Infinity series i need help also**

a = 20 r = 3/5 S = 20/(1 - 3/5) Better review you geometric series material.
*October 14, 2015*

**math**

the like terms are those involving the same variable, in this case, y So, (A)
*October 14, 2015*

**MATH**

pick the one where no x-value (1st element) is repeated. Sadly, not D. You cannot have f(5) = 4 and also f(5) = 1.
*October 14, 2015*

**Maths**

g(0) = (-1)(2)(-a)(-b) = -2ab g(3) = (2)(5)(3-a)(3-b) (3-a)(3-b) = 4 9-3a-3b+ab = 4 9-3(a+b)-2 = 4 -3(a+b) = -3 a+b = 1 (a+b)^2 = a^2+b^2+2ab = a^2+b^2-4 = 1 a^2+b^2 = 5 Now it should be clear what a and b are.
*October 14, 2015*

**math**

well, work = force * distance, so ...
*October 14, 2015*

**MATH**

1A 2B 3C 4B
*October 14, 2015*

**Math**

I guess you do. -^90 is pure garble. If you have an exponent, it goes in between the numbers, as PsyDAG showed you.
*October 14, 2015*

**MATH**

well, let's see 1=√1 2=√4 3=√9 4=√16 5=√25 So, do you still think √6 is between 4 and 5?
*October 14, 2015*

**Algebra**

-4(-3x+w)+6(-6w+2x) 12x-4w-36w+12x ...
*October 14, 2015*

**Math**

well, √(49+64) = √113 Is 5.4 still your choice? and what the heck is approxir???
*October 14, 2015*

**7th Grade Maths**

(10/1.5)*10 If she jogs 2 times as far, it will take 2 times as long, and so on. That's why the above works.
*October 14, 2015*

**college algeb**

try them yourself, and then see what wolframalpha.com does. For example, #3 is http://www.wolframalpha.com/input/?i=x^2-3x-10+%3E%3D+10
*October 14, 2015*

**calculus**

See if you can get what wolframalpha.com gets: http://www.wolframalpha.com/input/?i=%28%2818x^2-6y%28%286x^3-3y^2%29%2F%284xy%2B1%29%29%29%284xy%2B1%29+-+%286x^3-3y^2%29%284y%2B4x%28%286x^3-3y^2%29%2F%284xy%2B1%29%29%29+%29%2F%284xy%2B1%29+^2
*October 14, 2015*

**calculus**

oops. The denominator is (4xy+1)^2
*October 14, 2015*

**calculus**

3x^4-4xy^2+7=2y 12x^3 - 4y^2 - 8xyy' = 2y' (8xy+2)y' = 12x^3-4y^2 y' = (6x^3-3y^2)/(4xy+1) y" = (18x^2-6yy')(4xy+1) - (6x^3-3y^2)(4y+4xy') ------------------------------------------------------- (4xy+1) Now it's just algebra. Substitute the ...
*October 14, 2015*

**differential calculus**

Using similar triangles, if the man is x from the light, and his shadow is h tall, h/40 = 6/x 1/40 dh/dt = -6/x^2 dx/dt So, when the man is 10 ft from the light, 1/40 dh/dt = -6/100 * 4 dh/dt = -9.6 ft/s
*October 14, 2015*

**algebra**

a+5d=21 17/2 (2a+16d) = 0 The sequence is 56, 49, 42, 35, 28, 21, 14, 7, 0, ...
*October 14, 2015*

**math**

are we using linear cooling, or Newton's law?
*October 14, 2015*

**Math**

(x+4)5 = 3(x + x+2)-6 Now just find x, the smallest number.
*October 14, 2015*

**Logarithm help please**

shouldn't there be an x somewhere in the formula?
*October 14, 2015*

**Math**

5/8 x = 3/5 (x+1) x/(221-x) = 8/9 It also helps to know that 221=17*13
*October 14, 2015*

**Calculus**

huh? it's not (e^3t)^6 = (e^2t)^9 6e^3t = 9e^2t e^t = 9/6 t = log 1.5
*October 13, 2015*

**MATHS**

3x^2+3tx-xyt-t^2y 3x(x+t) - yt(x+t) that help?
*October 13, 2015*

**precalc**

Hints: sec-cos = 1/cos - cos = (1-cos^2)/cos csc^2 cos^ = (1/sin^2)cos^2 = cot^2 sin/csc = sin^2 and cos/sec = cos^2
*October 13, 2015*

**MATHS**

(2j)^-1 = 1/(2j) (p/6)^-3 = (6/p)^3 = 216/p^3
*October 13, 2015*

**Algebra**

Well, you have the rule, so you know that t(1) = 3*25 t(n+1) = t(n)*25 so, t(n) = 3*25^n
*October 13, 2015*

**Algebra 2**

50+35x = 190
*October 13, 2015*

**Algebra 2**

since x=y+2, (y+2)+2y=17 ...
*October 13, 2015*

**Math**

If you want to find x so that 2/3 > 3/x, then just multiply both sides by 3x and you have 2x > 9 Can you do that now?
*October 13, 2015*

**Calc**

well, after t hours, the plane has gone 420t miles. So, the distance z is found using z^2 = 2^2 + (420t)^2 so, that means that z is changing at 2z dz/dt = 2*420^2 t now just plug in your numbers.
*October 13, 2015*

**Math**

Just expand things, collect terms, and solve for x: 4x(x-2)=(2x+1)(2x-3) 4x^2-8x = 4x^2-4x-3 Now go for it!
*October 13, 2015*

**Algebra 2**

clearly, since 7 is subtracted for each term, An = 17-7(n-1)
*October 13, 2015*

**Algebra 2**

just multiply both sides by 5x and then go for it.
*October 13, 2015*

**Math**

a relation is not a function if one value of x maps to more than one value of y. So, which relation has unique 1st elements for all its pairs?
*October 13, 2015*

**Math**

7^-2 = 1/7^2 = 1/49 2.28x10^8 is what you wrote 2.28x10^-8 = 0.0000000228 The others look good. Watch out for those negative powers.
*October 13, 2015*

**Math**

well, 324 = 108 * 3
*October 13, 2015*

**Simple Interest**

The interest for n days is 665 * 0.099/365 * n So, figure out how many days of interest he has to pay.
*October 13, 2015*

**Math**

I agree. Of course, the mere presence of a variable does not mean it's open. 2y+3 = 2y+3 is true for any y 2y+3 = 2y+2 is false for any y
*October 13, 2015*

**precalc**

well, (1+tan)/sin = (1 + sin/cos)/sin = (cos+sin)/(sin cos) That should get you going...
*October 13, 2015*

**Geometry 1 question**

Invalid The converse is not necessarily true. There may be lots of kids dismissed early who do not play sports at all.
*October 13, 2015*

**Calculus**

well, v = at so, what is t when -16t^2 + 96t = 128? Pick the lowest value, since you want the ball on its way up. Now plug that in to find v at that time.
*October 13, 2015*

**Math**

how much work is done each hour? 1/30 + 1/40 = 1/x It will take them x hours working together. Actually, the problem is very poorly worded, since the times are for shoveling their own driveways, and we have no idea which driveway they work on together.
*October 13, 2015*

**pre-cal**

a little synthetic divsion shows that the remainder of the division is 3-k. We wan the remainder to be zero, so k=3 and we see that x^3-kx^2+x+5 = (x+1)(x^2-4x+5)
*October 13, 2015*

**pre-cal**

assuming c is real, the we also need to have x-i as a root. That means that x^2+1 must divide it. A little synthetic division shows that the remainder is c-9. The remainder must be zero, so c = 9. x^4+10x^2+9 = (x^2+1)((x^2+9)
*October 13, 2015*

**math**

I think you mean an ant weighs 2*10^-5 lbs. So, the ants weigh 2*10^-5 * 1*10^15 = 2*10^10 lbs
*October 13, 2015*

**Math**

C is the converse, and it is clearly false. 11 < 15 but 11 ~< 10 The other statements may be true or false, but they are not the converse of the given statement.
*October 13, 2015*

**achimota secondary school**

(11+x)(3)=45
*October 13, 2015*

**college algebra**

Since revenue = quantity*price, after x 1-cent reductions, the revenue is r(x) = (600+20x)(0.50-0.01x) Now use that to answer the questions.
*October 13, 2015*

**Math**

If the dimensions are x,z, with z being the height, then x^2 z = 78, so z=78/x^2 The cost c is c(x,z) = .30x^2 + 4(.10xz) + .20x^2 But, z=78/x^2, so c(x) = .30x^2 + .4x(78/x^2) + .20x^2 c(x) = .50x^2 + 31.2/x Now that's not easy to do algebraically, but with a little ...
*October 13, 2015*

**math**

each draw there are 10 marbles. So, P(pink,pink) = 3/10 * 3/10
*October 13, 2015*

**Math**

well, is it true for y=0? Is it true for y=2.5? So, ...
*October 13, 2015*

**math**

2*(m)^2*(p) 2*(-5)^2*(-4) = 2*25* -4 = -200 (-5)^2 = 25 is not the same as -5^2 = -25 Gotta watch the order of operation. powers are done first
*October 13, 2015*

**Calculus**

well, what is t when s=0? Use that value to calculate v(t) = -32t-32
*October 13, 2015*

**math**

Both look good to me.
*October 13, 2015*

**Calculus 1**

Assuming you meant x=0, g'(x) = 1/3 (1+x)^(-2/3) g'(0) = 1/3 So, the line going through (0,1) with slope 1/3 is ? See http://www.wolframalpha.com/input/?i=plot+y%3D%281%2Bx%29^%281%2F3%29%2C+y%3Dx%2F3%2B1+for+-1%3C%3Dx%3C%3D2
*October 13, 2015*

**Math**

.33
*October 13, 2015*

**math**

just get out your calculator and convert them all to decimals. Then it will be easy to sort them out.
*October 13, 2015*

**Surd help plz**

well, √59300 = √(5.93*10^4) = √5.93 * 10^2 . . .
*October 13, 2015*

**Math**

#1 is ok five times k = 5k you did k divided by 5 3t+s = 45, but 3(3t+s)=135 2s-t = 2*9-12 = 18-12 = 6 You did 2t-s
*October 13, 2015*

**Math**

No, the domain is [3,8)U(8,∞)
*October 13, 2015*

**Math**

Sarah is correct in concluding that the domain of √(2x-3) is [3, ∞). But x-8 = 0 when x=8 division by zero is not defined 8 is not in the domain, so [3, ∞) cannot be the domain, since it includes 8. So, what is the domain?
*October 13, 2015*

**Math**

10d + 25(d-4) = 600 Now just solve for d, and you can figure the rest.
*October 13, 2015*

**Mathematics**

10 fruits 5 bananas P(banana) = 5/10
*October 13, 2015*

**Maths**

recall that y' is the slope of the tangent line. The slope is the tanθ, so y'(x) = 4x^3-3x^2+7 y'(2) = 4*8-3*4+7 = 27 = tanθ θ = 87.9° The line x-2y-1=0 has slope 1/2 So, where is y' 1/2? y' = 2x-3 2x-3 = 1/2 when x = 7/4
*October 13, 2015*

**Calculus 1**

remember your trigh identities: tanh = sinh/cosh sech^2 = 1-tanh^2 and so on.
*October 13, 2015*

**Calculus 1**

sounds about right.
*October 13, 2015*

**Calculus 1**

good. just enter your expression, and it will evaluate it. Bookmark that site!
*October 13, 2015*

**Calculus 1**

what, you don't have a calculator? Or an online one, such as wolframalpha.com? I mean, geez...
*October 13, 2015*

**5th grade Math**

technically, it's 5(600+400) By moving the 5, you also tossed in a commutative property of multiplication.
*October 12, 2015*

**Math**

it is the original number. Write down your fractions, and then you can see how the factors and units cancel.
*October 12, 2015*

**MATH**

The average rate of change is change-in-y ------------------ change-in-x So, you have Between (3,11) and (6,65): (65-11)/(6-3) = 54/3 = 18 (b,m) and (s,u): (u-m)/(s-b) (x, f(x)) and (x+h, f(x+h)) [f(x+h)-f(x)]/h
*October 12, 2015*

**math**

21:(7/9) = 21/(7/9) = 21*9/7 = 3*9 = 27/1
*October 12, 2015*

**Geometry**

no, because 23 is not divisible by 3! You want B, because 27 is divisible by 3, but not divisible by 6.
*October 12, 2015*

**Logarithm help**

each year the value is 0.85 as much. So, after t years it is worth .85^t as much. So, you want t when .85^t = 0.5 Now take the log of both sides: t log .85 = log .5 t = (log .5)/(log .85) = 4.26
*October 12, 2015*

**Algebra 2**

Your product matrix is correct. p12 is the element in row 1, column 2: 6 Looks like you need to review the introductory material on matrix notation!
*October 12, 2015*

**urgent physics help**

you know that s = rθ Plug in your numbers. Remember that θ is in radians, which your value clearly is not.
*October 12, 2015*

**Math**

start off with 121 212 ----- 333 as long as there is no carry, things should work fine.
*October 12, 2015*

**math**

In that case, play around here: http://davidmlane.com/hyperstat/z_table.html You can see how it all works. It amazes me how students can get online for help, and not use the amazing resources that are available with just a little help from google.
*October 12, 2015*

**math**

so, do you have a Z table to consult? What did you find?
*October 12, 2015*