Friday

April 18, 2014

April 18, 2014

Total # Posts: 21,761

**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.

**Math 2**

w is 1,2,3,4,5 v = 2*5*w = 10w, so possible values are 10,20,30,40,50

**math**

s^2 = r^2 + h^2 = 16+81 = 97 s = 9.8

**Math 2 questions**

5.7 x/4 = 20/10 x = 8 you are correct. Too bad it was a guess, not the result of calculation.

**plane geometry**

a = 1/2 r^2 (θ-sinθ) 4.3 = 1/2 * 4 (θ-sinθ) θ-sinθ = 2.15 Solve using your favorite numerical or graphical method to get θ = 2.63511

**Math help plz check my answers!**

It is, in fact, A a rectangle can be long and skinny, 4 sides not equal.

**Math - Nope**

Bzzt. no two sides of a trapezoid have to be equal. Think harder.

**Math help plz check my answers!**

and we have a winner!

**Algebra 1 Answer Check**

looks good to me

**math**

95 said something 70+45=115, so 20 said both

**math**

If he bought x in January, 2x+3 = 15 x=6

**Physics**

solve 2π√(L/g) = 1/7

**Alegbra**

-7-2z^3+4y -12-3z^3+6y --------------- -19-5z^3+10y

**Alegbra - eh?**

they're already in scientific notation.

**Alegbra**

36.92x10^(13-22) 36.92x10^-9 3.692x10^-8

**math**

you must have some examples in your text. You can get some good info here: http://www.purplemath.com/modules/plane2.htm

**Math**

assuming you want to expand the product, you get 6p^2 + 29p + 9 Play around some at calc101.com -- click on the long multiplication button. multiplying polynomials is just like multiplying numbers, where the power of the variable is like the 1s,10s,100s,... columns in numbers....

**Math (check answers)**

I think 1A would be in cm, not meters. A pencil is rather short. The others look ok.

**Pre-Algebra**

i agree

**multiplication**

well, is 2*3 at least 7?

**Music help**

The minor key starts three semitones below its relative major, so A major -> F# minor 5# = FCGDA, so key = B

**math**

for this, you need to recall that the perpendicular bisector of a chord goes through the center of the circle. So, if you can find two of the bisectors, they will intersect at the center. To find the bisectors, locate the midpoint of a chord, then find a line perpendicular to ...

**Math**

Take a look at http://www.jiskha.com/display.cgi?id=1394471353 and plug in your points instead

**Math - hmmm**

Actually, the above is true only if DF=DG. I think there's something missing here.

**Math**

No idea where O is, but if you meant FG=15x, then since FDG = FDE, FE=FG, so 9x+114 = 15x 4x = -114 x = -26

**algebra 1**

42

**Math**

2^x = 10^5

**programming**

total=0 n=10 for (i=1..n) total += test[i] avg = total/n

**math - incomplete**

no function given.

**trig**

h/80 = sin 40°

**algebra**

4y + 5y^2 + 2y^3 - 8y^2 collect like powers to get 2y^3 - 3y^2 + 4y

**Calculus**

Since the derivative is the slope of the tangent line, we need -2sinx - 2cosx*sinx = 0 -2sinx(1+cosx) = 0 sinx = 0 means x = nπ cosx = -1 means x = (2n+1)π so, f(x) has a horizontal tangent at x=nπ

**math**

1098

**math**

y = -5(x-1)^2 + 4

**math**

the 13x in the middle indicates you will need 5 as one of the factors of 20, and it cannot be multiplied by 2, so (2x+5)(x+4)

**Calculus Help**

3/31: t=90 4/21: t=111 L'(t) = 2.8cos[(2π/365)(t − 80)](2π/365) now just plug in t=90 and t=111 The answer, of course, will be in hr/day.

**math**

we know that x+1 = -x+7 x=3 so the base is 6

**Math**

2/5 of males = 2/5 * 30 = 12 That should help.

**Math**

2 pi *10 inches per hour

**Math**

(1610-1250)/(3*10)

**Math**

x(1/2 + 1/4 + 1/9) = 62

**Math**

150 * 3 * 1/2 * density.of.snow

**Math**

x+y = 3/2 x-y = 5/12 2x = 11/12 ...

**Math**

C MN and PR are not corresponding sides

**MATH TRIGO-PLSSS ANSWER CLEARLY COZ IM VERY LOW IN**

Draw a diagram. Let T be the top of the tower M be the top of the monument A be the base of the tower B be the base of the monument ∠TBA = 31° so, 145/TB = sin 31° Since ∠TBM = 59° ∠MTB = 18°, ∠TMB = 103° The desired height (MB) is f...

**algebra**

c(p) = 50+2p

**algebra**

well, is (2+3)^2 = 2^2+3^2 ? Hint: (x+y)^2 = (x+y)(x+y) expand that and compare to x^2+y^2

**math**

take a look at http://www.wolframalpha.com/input/?i=3%28x-4%29^2+-3+

**math**

since there are 5 choices for each digit, there are 5^8 choices for the number

**Math**

if the initial value is v, v - .35(2) = 13520 Now, knowing v, after n years the car is worth v(1 - .35n) Note that the car is fully depreciated after only 3 years, if the depreciation is 35% of the full value each year.

**math trig**

If B is at distance x from the tower of height h, h/x = tan 46° h/(x+80) = tan21° so, eliminating x, we get h/tan46° = h/tan21° - 80 Now just solve for h

**MATH :DD**

2(5+.12(m-200)) < 30 minimum? 0 of course.

**Maths**

x = (y-3)/5 d = (c+2)/5 a = (v-u)/t

**science**

neutral must have 11 so, the +1 ion has only 10 electrons p+n = 23 p = atomic number

**science**

an ion has unbalanced charge, so what do you think?

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