Monday

April 21, 2014

April 21, 2014

Total # Posts: 21,815

**math**

best to use shells here: v = ∫[0,2] 2πrh dx where r = 3-x and h = y = x^3 v = 2π∫[0,2] (3-x)x^3 dx Simply polynomial, so just plug and chug.

**pragati**

a = (42+54)/2 * √(19^2 - 12^2)

**math**

You won't find any diagrams here, but division is just a shorthand way to subtract. 2.6/.4 tells you how many times you can subtract .4 from 2.6 without passing zero. 2.6 - .4 = 2.2 2.2 - .4 = 1.8 1.8 - .4 = 1.4 1.4 - .4 = 1.0 1.0 - .4 = 0.6 0.6 - .4 = 0.2 Now you must sto...

**Calculus Help**

#1: 2y y' = 2x + 0 #2: 2y y' + ay' = 2x + a + 0 just solve for y' in each case.

**math**

what's the smallest number that is a multiple of both 2 and 3? And for 8 and 10?

**Algebra**

slope is (-8-4)/(3 - -3) = -2 Now plug in the point-slope form: y-4 = -2(x+3) Now it's easy, right?

**science pls help**

correct. At least it appears you can match up the provided answers with the lists of choices...

**science pls help**

Looks like you need to brush up on one of the most basic and useful identities in mechanics: F = ma F(N) = m(kg) * a(m/s^2) 1 N = 1 kg-m/s^2 So, with that in mind, #1: F = ma = 40kg * 10m/s^2 = 400 kg-m/s^2 = 400N #2: F = ma = 60kg * 2m/s^2 = 120N Note that you can eliminate t...

**Math**

after n hours, 1+3+3^2+3^3 + ... + 3^n = (3^n - 1)/2 people have heard the joke. So, we want n such that (3^n - 1)/2 = 8500 3^n = 17001 n = 8.8666 hours = 8 hrs 52 min

**Math**

7*8*4 = 56*4 = 224 recall that using a variable, 7x * 8x * 4x = 224x^3 Now, using units, 7ft * 8ft * 4ft = 224 ft^3

**Math**

did you multiply the three dimensions? If so, what did you get? If not, what's the problem?

**Math - Answer Check**

I'd say #15 is right, since you were given 180,000 inches. 2.84 miles is close enough, IMO.

**Math - Answer Check**

#12. a mile is 5280 ft, not 5820 The rest look ok (including #15!)

**MATH**

1/5 is correct 1/4 may be correct, but only if there is exactly one white sweater in the bunch.

**Pre-Calculus**

r = 5sinθ r^2 = 5r sinθ x^2+y^2 = 5y x^2 + (y - 5/2)^2 = 25/4

**Pre Calculus**

rcosθ = 3 r = 3secθ

**MATH**

but 1 is not a prime. It is explicitly excluded from the list of primes.

**Geometry**

recall that if the legs of a right triangle are a and b, and the hypotenuse is c, then the Pythagorean Theorem states that a^2 + b^2 = c^2 So, the height of the triangle is 12 There are several commonly used right triangles which you would do well to commit to memory: 3-4-5 5-...

**Geometry**

5^2 + height^2 = 13^2

**Which compound is made up of three elements?**

Do you know how to count the elements in a chemical formula?

**algebra**

hint: y = -4/6 x + 2

**math**

Hmmm. of the 11 numbers, how many are NOT 23?

**math**

So, P(violet, pink, or blue) = V+P+B

**math**

assuming that what was meant is that the jar contains ONLY green and purple marbles . . . I think we can say that, but it's also possible that other marbles were not mentioned. Read Heinlein's Stranger in a Strange Land. One of the characters is a professional observer...

**math**

correct

**Probability - Math**

total junior or seniors / total students (.16+.24)/1.00 = .40 Those who live in the dorm: (.16*.30 + .24*.20)/1.00 = .096

**Science**

hint: both correct choices involve only water

**math**

now you're cookin' (aside from that pesky 32!)

**math**

ummm, 6+7+26+13 = ?

**math**

number 2 is ok #1. Come on! The numbers are 1,2,3,4,5,6 only FOUR is divisible by 4! P(4) = 1/6

**math**

If there are 6 numbers on the die, how many of them are multiples of 4? I think not 2. How many numbers are there from 16-23? Remember to count both 16 and 23. #3 ok

**Calculus**

well, x^2/(2logx) = x^2/log(x^2), so if you can figure out the limit of x/logx, you're ok. Since x->0 and logx->-∞, x/logx -> 0/-∞ = 0 -------------- e^-x -> 0 as x->∞, so the upper limit -> 0 e^0 = 1, so the lower limit -> 2

**Math**

well, the factors of 18 are 1,2,3,6,9,18 The -21 in the middle makes me think that 2,9 will be likely, so (4x+9)(x-2) gives +x nope (2x+9)(2x-2) gives +14 Hmmm. That pesky 4. So, (4x+3)(x-6) : -21x YAY!

**Math**

after the 1/3, she had 2/3 left 1/2 of that is another 1/3, so if she started out with x, x - x/3 - x/3 = 6 x = 18 check: she spent 6, had 12 left. she lost half of 12, or another 6, leaving her with just 6.

**Math**

yes

**Math**

assuming the velocity is as written, a = 3(2) = 6 If you meant 3(2t+1)^0.4, then a = 2.4/(2t+1)^0.6 as usual, s = 25 + 1/2 at^2 = 25 + 3t^2 or = 25 + 1.2(2t+1)^1.4 just plug in your values.

**Calc Help :(((((**

d/dx(x) = dx/dx = 1 So, how come you included it in d/dx (x+3) but not in d/dx (x-8)? Your work so far is correct. 3(x+3)^2(x-8)^5(d/dx(x))+5(x+3)^3(x-8)^4 3(x+3)^2(x-8)^5 + 5(x+3)^3(x-8)^4 Now factor out some stuff: (x+3)^2 (x-8)^4 (3(x-8)+5(x+3)) (x+3)^2 (x-8)^4 (8x-9)

**math**

find the factors. If any of them is zero, the product is zero. Sometimes the factors are hard to find, and sometimes there are none using just real numbers. For higher than quadratics, it starts to become necessary to use various numerical methods.

**math**

I would assume it means to divide each third into two pieces (presumably also equal halves)

**math**

avg speed is total distance divided by total time: (5+4)/(21+39) km/min = 9 km/hr That's a pretty good clip!

**Science URGENT**

Since 1 mole of S8 reacts with 4 moles of Cl2, .779 moles S8 will need 3.116 moles of Cl2, but you only have 1.410 moles Clearly the Cl2 is lacking here.

**Science asap**

#1 Looks like B to me D means that it doesn't rain till after the water has run off. Clearly it has to precipitate before the water is in the river.

**Chemistry**

It'd be Iron Nitrate, but more precisely, Iron (II) Nitrate

**CALCULUS HELP**

If we let u = 8x-3 v = 6x+7 then we can make the expression a little easier to read during the computational steps: f' = (5u^4*8*v^12-u^5*12v^11*6)/v^24 Now, you can cancel out v^11 top and bottom to get f' = (40u^4*v - 72u^5)/v^13 Now factor out 4u^4 to get f' = 4...

**math patterns and rules**

have you actually tried any of the proposed solutions?

**algebra**

hard to say, eh? what was the relation?

**math/algebra**

1 - 1/(x-1) - 2/(x+1)

**math**

First step -- talk to your teacher!

**Math**

20 times 10 = 200

**Calculus**

limit as x->2- = 5 limit as x->2+ = 5 since one-sided limits are the same, and f(2)=5, f is continuous Do you have to do the delta-epsilon limit proof?

**Calculusmath**

think. It's a circle. Invariant under rotation about its center.

**Precalculus II**

x = -5 + 11arccos(7^y-9) (x+5)/11 = arccos(7^y-9) 7^y-9 = cos (x+5)/11 7^y = 9 + cos (x+5)/11 y = log7 (9 + cos (x+5)/11) you know that sin π/3 = √3/2 so, 2kπ + π/3 or (2k+1)π - π/3 or (2k+1)(π/2)±(π/6) 1+cos(3x-π/4) = 1/2 c...

**math**

(x-6)(x+3)

**Calculus**

as usual, draw a diagram and you will see that if θ=0 when x=0, tanθ = x/4 so, sec^2θ dθ/dt = 1/4 dx/dt Now, you have θ and dθ/dt, so just solve for dx/dt

**Calculus**

At time t, using the law of cosines, d^2 = (7t)^2 + (5t)^2 - 2(5t)(7t)cosπ/4 = 74t^2 - 35√2 t^2 = (74-35√2)t^2 so, 2d dd/dt = 2(74-35√2)t Now, plug in your numbers to get d(15), and solve for dd/dt at t=15 Remember to use appropriate units

**algebra**

if so, y/x is constant 6.4/4 = 1.6 11.2/7 = 1.6 16/10 = 1.6 looks good, no?

**Calculus**

what you have tried is the volume when rotating the region about the x-axis. But, of course, the volume of a disk is pi r^2 dx, not pi r^3 dx In addition, your radius is 3-x, not y, since you are rotating about the line x=3, not y=0. So, if you want to use discs, you need to i...

**Calculus- typo**

64/6 + 8 + 20 - ( -64/6 + 8 -20 ) 64/3 + 0 + 40 184/3

**Calculus**

product rule and chain rule -- if y = uv y' = u'v + uv' Here u=csc^2 x and v = arccos(1-x^2) y' = -2 cscx cscx cotx arccos(1-x^2) + csc^2 x 1/√(1-(1-x^2)^2) * -2x kind of messy, no? well, recall that if cos u = 1-x^2, sin u = x, so we really have y = -csc...

**math**

13/150

**Math**

84 = pi * 36 * h now just solve for h same for the other

**Calculus Help**

just use the quotient rule and chain rule. If f = u/v f' = (u'v-uv')/v^2 f' = 5(8x-3)^4(8)(6x+7)^12 - (8x-3)^5(12)(6x+7)^11(6)]/(6x+7)^24 = -16(8x-3)^4(21x-31)/(6x+7)^13

**math studies**

The diagonals are perpendicular, and they bisect each other. So, you have 4 right triangles with legs 6 and 3.5 The diagonals bisect the vertex angles, so the angle is 2arctan(6/3.5)

**Algebra**

If a+b = c you cannot say that a^2+b^2 = c^2 √(9y - 196) + √196 = √49 √(9y - 196) + 14 = 7 √(9y - 196) = -7 But, √N is positive. So, you cannot have √(9y - 196) = -7 √x(√9 - 4/3) = √25 √x(3 - 4/3) = 5 √x(5...

**Algebra**

x=.10(100-x) x = 10 - x/10 11/10 x = 10 x = 100/11

**Chemistry - incomplete**

A good first step would be to get some H on the left . . .

**Math**

the difference is 32 votes Had 16 people voted differently, they'd both have had 228 votes. So, if at least 17 had voted differently, Susan would have won.

**Algebra**

There's no way that √28 + √63 + √175 = 6.06 You must have hit some wrong keys Just a rough approximation would be 5 + 8 + 13 = 26, not 6.06!

**Algebra**

#1 ok #2 ok if you meant √(6p+1) #3 √28 + √63 + √175 2√7 + 3√7 + 5√7 = 10√7 #4 √(2w+5) + 4 = √25 √(2w+5) = 1 2w+5 = 1 2w = -4 w = -2 #5 √18/√(8-3) 3√2 / √5 (3√10)/5 If you meant ...

**Algebra**

check the discriminant #1: b^2-4ac < 0, so no solutions #2: b^2-4ac = 0, so one solution

**Algebra**

let's say that f(x) = a√x + b Then we know that a√1 + b = -2 a√5 + b = 0 a(√5-1) = 2 a = 2/(√5-1) = (√5+1)/2 b = -2 - (√5+1)/2 = -(√5+5)/2 f(x) = (√5+1)/2 √x - (√5+5)/2 Somehow I don't think that's w...

**Mathh**

squares: 1 4 9 cubes: 1 8 27

**math. plzz help**

√(3^2+5^2) = √34 so the slant height is 5.8 √(10^2+4^2+10^2) = √216 = 14.7 √(14^2+3^2+4^2) = √221 = 14.9

**Algerbra**

factors of 18 which differ by 3 are 3 and 6, so w(w-6)(w+3)

**Math**

If Ling, suitcase, and backpack weigh x,y,z, respectively, then we have x = 3y y = z+20 x+y+z = 170 so, 3y + y + y-20 = 170 5y = 190 y = 38 So, Ling weighs 114 suitcase: 38 backpack: 18

**math**

(100*40+(53-83))/100 = 39.7

**chemistry**

each mole of CaCO3 produces 1 mole of CaO so, convert grams CaO to moles, then back to grams of CaCO3

**math**

(22.8+9.5)(1800/285)(3.49) = $711.96

**math**

158-110 = 48 degrees so, it will take 96 seconds

**math**

12-23-10-74-77

**Algebra 1**

units: 0-8 tens: 1-9,2-9,...8-9,9 9+8+7+...+1 = 45

**algebra**

if there were a adults, there were 2a children, so 8*a + 5*2a = 648 18a = 648 a = 36 36 adults and 72 children

**Math**

2 walls are 9x8 2 walls are 7x8 ceiling is 9x7 2(2*9*8 + 2*7*8 + 9*7)/275 = 2.32 so, 3 cans of paint

**math**

3^n: 1,3,9,27 so, which is 5 times that? Hint: only one sequence starts with 5

**math**

p'(1)=0 so max or min p"(1) < 0, so concave down: a max (A)

**math**

we know x is not going to infinity, so the asymptote must be vertical. (D)

**math**

x(6x+1) < 15 6x^2 + x - 15 < 0 now you have a parabola. You need to find where it crosses the x-axis, and between those two points, it will lie below the x-axis. (2x-3)(3x+5) < 0 so, the roots are at x = -5/3 and 3/2 Between those two values, the parabola lies below t...

**Algebra II**

√(-24 - 10i) If you want to find a perfect square which equals -24-10i, it will have to include -5i, so (a-5i)^2 = -24-10i a^2 - 10ai - 25 = -24-10i Hmmm. Looks like a=1 (1-5i)^2 = 1 - 10i - 25 = -24-10i So, √(-24 - 10i) = 1-5i or -1+5i Or, if you use polar form, y...

**rational expressions**

not sure what you are after Do you mean the equation must use two different expressions, both of which are equal to the given value, or do you mean the equation must use two rational expressions, and the result is the given value? as in 1/(2x+1) - 3x/(x^2+5) = (x+5)^2

**calculus**

The circle in the x-y plane is x^2 + (y - a/2)^2 = a^2/4 x^2 = a^2/4 - (4y^2-4ay+a^2)/4 = (y^2-ay)/4 The limits of integration in the x-y plane are 0 < y < a 0 < x < (1/2)√(y^2-ay) then use symmetry and multiply by 4

**Algebra 1 Answer Check**

Looks good to me.

**algebra**

6n-(-10) = -20 6n = -30 n = -5

**Math**

a = pi * (25/2)^2 Nothing was said about lawn furniture (or tents).

**Math (check answers)**

I think #1 is D to convert from cm to m, you divide by 100

**math**

could be any of the choices, depending on the unseen and unexplained diagram.

**Math**

no diagram, but if angles 1,2,3 are consecutive vertices, then 15x + x+y = 180 x+y + 3z = 180 15x = 30z Nope; impossible answer. So, some explanation is needed

**Geometry**

17x = 408 x = 24

**Calculus**

the answers are the same √[(x-3)/2] = √[(x-3)/2 * 2/2] = √(2x-6)/2

**Math 2**

360 = 10*36 The factors of 36 are 1,2,3,4,6,9,12,18,36 Pair them up to get your answer.

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