Thursday

October 27, 2016
Total # Posts: 45,377

**Parabola**

2x^2-3x+4y+5=0 2x^2-3x+5 = -4y x^2 - 3/2 x + 5/2 = -2y x^2 - 3/2 x + (3/4)^2 = -2y + (3/4)^2 - 5/2 (x - 3/4)^2 = -2y - 31/16 (x - 3/4)^2 = -2(y + 31/32) So, the vertex is at (3/4, -31/32) You know that for the parabola x^2 = 4py here, 4p = -2, so p = -1/2 the focus is at a ...

*September 28, 2016*

**math**

the exterior angles of a decagon are all 360/10 = 36° So, 3x+6 = 36 x = 10 For the interior angles (each 144°), 3x+6 = 144 x = 46

*September 28, 2016*

**maths need help**

you will not solve this algebraically. Use a numeric approximation or read it from a graph, such as http://www.wolframalpha.com/input/?i=150sinx%3Dx%2B69.98

*September 28, 2016*

**algebra 1, solving polynomials**

there are no zeros. All you have is 8*12

*September 28, 2016*

**algebra**

1st step: multiply both sides by 17

*September 28, 2016*

**Urgent Math**

discs of thickness dx: v = ∫[0,1] πr^2 dx where r=y = 1-x^2 v = ∫[0,1] π(1-x^2)^2 dx shells of thickness dy: v = ∫[0,1] 2πrh dy where r=y and h=x=√(1-y) ∫[0,1] 2πy√(1-y) dy To integrate, use u^2 = 1-y dy = -2u du

*September 28, 2016*

**calculus help me**

y = cot(x+y) y' = -csc^2(x+y) (1+y') y' = -csc^2(x+y) - csc^2(x+y) y' y' (1+csc^2(x+y)) = -csc^2(x+y) y' = -csc^2(x+y)/(1+csc^2(x+y)) But, csc^2 = 1+cot^2, so y' = -(1+y^2)/(1+1+y^2) = -(1+y^2)/(2+y^2) or, you can say 1/y = tan(x+y) arctan(1/y) = x+...

*September 28, 2016*

**algebra**

good answer, but it does not address the question.

*September 28, 2016*

**math**

since distance = speed * time, 90(t-1) = 80(t+1)

*September 28, 2016*

**Maths**

sin^-1 (4x^4+x^2) = 1/6 pi 4x^4+x^2 = sin(pi/6) = 1/2 8x^4+2x^2-1 = 0 x^2 = [-2±√(4+32)]/16 = [-2±6]/16 = -1/2 or 1/4 x^2 = -1/2 x = ±i/√2 x^2 = 1/4 means x = ±1/2

*September 28, 2016*

**science**

F=ma, so 5 = 18M = 24m M = 5/18 kg m = 5/24 kg For both masses, 5 = (5/18 + 5/24)a a = 72/7 m/s^2

*September 28, 2016*

**Aptitude**

how many times around does each hand go? Each time around has circumference 2πr for the hand's radius.

*September 28, 2016*

**math trig**

see related questions below. Just use your numbers to follow the logic.

*September 28, 2016*

**Maths**

in English you don't lend from. You either borrow from or lend to fix that and all the other typos and try again.

*September 28, 2016*

**Calculus**

#1 You know that as x->0 sinx/x -> 1 tanx/x -> 1 You have θ/tan7θ = (1/7) (7θ/tan7θ) -> (1/7)(1) = 1/7 As the graph will show http://www.wolframalpha.com/input/?i=plot+y%3Dx%2F(tan7x),+-0.3+%3C%3D+x+%3C%3D+0.3 #2 some parentheses would help f(x...

*September 28, 2016*

**Math**

at r%, 8000(r/100) = 12000((r-1)/100) - 200

*September 28, 2016*

**Math**

8000(r/100) = 12000((r-1)/100) - 200

*September 28, 2016*

**Math**

A plug in t=0 B as with any parabola, the vertex is at t = -b/2a C see B D plug in t=2

*September 28, 2016*

**Math**

(a) and (b) look ok distance = speed * time, so since the time is the same (3.5 hrs), just add up all the speeds and multiply by 210 minutes: 210(8/80 + 6/42 + 15/75) = 93 miles

*September 27, 2016*

**calc**

#1: h(x) = k cos x 0 ≤ x ≤ 3π #2: h(x)= 10 − x 3π < x #2: limit as x->3π = 10-3π #1: h(3π) = k cos3π = -k So, you need -k = 10-3π k = 3π-10 #1: h(x) = (3π-10)cosx

*September 27, 2016*

**math**

what are path numbers?

*September 27, 2016*

**math**

slope: (-4-5)/(-2-1) = -9/-3 = 3 Now, using the point-slope form, y-5 = 3(x-1) at x=0, y=2 2*3+2 = 8 2(3+2) = 10 You took twice the sum of the slope and the intercept, but that was not the question.

*September 27, 2016*

**Calculus**

who needs a limit? f = x + 4/x f' = 1 - 4/x^2 So, f'(4) = 1 - 4/16 = 3/4 The tangent line at (4,5) is thus y-5 = 3/4 (x-4) using the limit f(4+h)-f(4) = (4+h)+4/(4+h) - (4 + 4/4) = ((4+h)^2+4)/(4+h) - 5 = ((4+h)^2+4-5(4+h))/(4+h) = (h^2+3h)/(4+h) = h(h+3)/(h+4) Now ...

*September 27, 2016*

**algebra**

well, it traveled 90 miles in 1 1/2 hours. So, it is still 1 1/2 hours away at 2:15

*September 27, 2016*

**mathematics**

see related questions below

*September 27, 2016*

**Math**

87 - 6 - x >= 32 81 - x >= 32 49 >= x so, at most $49 for shirts.

*September 27, 2016*

**math**

Plot the points. It will be clear that the line contains (0,-50). Or, now that you know the slope, use the point-slope form of the line with any of the points. How about (5,80) y-80 = 26(x-5) Now plug in x=0 and you will get y = -50.

*September 27, 2016*

**math**

no idea what you did wrong, since you didn't bother to show your work.

*September 27, 2016*

**math**

first, check to be sure there is a constant slope: (80+310)/(5+10) = 26 (262-80)/(12-5) = 26 (444-262)/(19-12) = 26 So, the slope is 26 For the y-intercept, since x=0 is 1/3 of the way from 5 to -10, the y-intercept is 1/3 of the way from 80 to -310: -50 26 + -50 = -24 Just to...

*September 27, 2016*

**Algebra**

you cannot tell by looking at that table?? Really??? Look again.

*September 27, 2016*

**Math**

Let the amounts of notes be u,v,w,x respectively. Now just start writing down the facts: 100u+50v+20w+10x = 14400 x = 3w w = 5v v = 5u Now just solve for u. Or, consider if there is a single $100 note. That means there are 5 $50's, 25 $20's, 75 $10's 100+5*50+25*20...

*September 27, 2016*

**Science**

work is in Joules, J J = F*d = ma*d= kg-m^s/2 * m = kg-m/s Note I have used kg instead of grams, since MKS uses m,kg,s CGS uses cm,g,s You can use g,m,s if you want, but then the work will not be measured in Joules or ergs.

*September 27, 2016*

**Math**

3m wide, but how long? Anyway, if it is x meters long, then you need 3x - (3-2w)(x-2w) = 3x/2 because the area of the whole thing minus the area inside the pathway is the area of the pathway. So, plug in your length for x, and then solve for w.

*September 27, 2016*

**Math**

the width+length must be 12. So, start listing pairs of integers which add to 12: 1,11 2,10 ... 6,6

*September 27, 2016*

**Math**

twenty tens means a 2 in the hundreds place now work from that, one item at a time.

*September 27, 2016*

**math**

26 = 5+(3^2-6)*7 play around with the others a while. There aren't that many places to put the parens.

*September 27, 2016*

**Algebra**

see http://www.jiskha.com/display.cgi?id=1474984965

*September 27, 2016*

**math**

the length + width must be 12, so the following dimensions will work: 1x11 2x10 ... 6x6

*September 27, 2016*

**Algebra**

correct But note that x is a variable name × is the multiplication symbol

*September 27, 2016*

**Maths grade 8**

If there are n sides, then each exterior angle is 360/n degrees. each interior angle is thus 180 - 360/n = 180(n-2)/n degrees.

*September 27, 2016*

**de~movire**

note that x^4-x^3+x^2-x+1 = (x^5+1)/(x+1) see what you can do with that...

*September 27, 2016*

**math**

since distance = speed * time, 3x = 2.5(x+2)

*September 27, 2016*

**stationary point**

You need both partials to be zero. That is, #1: 3y^3 + 2xy = 0 #2: 3(3x+1)y^2 + x^2 = 0 From #1, we get x = -3y^2/2 Plug that into #2 and you get y^2 = 4/15 So, z has stationary points at (-2/5, ±2/√15)

*September 27, 2016*

**Math**

2x^2 - 128 = 0 x^2 = 64 x = ±√64 = ±8

*September 27, 2016*

**Math**

56/(77-56)

*September 27, 2016*

**mathematics need help**

There are lots of proofs of the chain rule on line. You can find one here, if you scroll down some http://tutorial.math.lamar.edu/Classes/CalcI/DerivativeProofs.aspx So, now you know that if y = f(g) and g is a function of x, then dy/dx = df/dg * dg/dx You can see that treated...

*September 27, 2016*

**mathematics need help**

this is just the chain rule. I assume you have seen the proof of that. That said, just substitute x for f(x).

*September 27, 2016*

**Physics .. hard problem**

oops. After falling for 5.88 seconds, the student is caught, then 3.81 seconds later they land gently on the ground.

*September 27, 2016*

**Physics .. hard problem**

At time t=x, the Rocketeer catches up with the student. At that point (the Rocketeer having arrived with some unknown velocity v), their height and speed are student: 427 - 4.9x^2 9.8x Rocketeer: 427 - v(x-5) - 4.9(x-5)^2 v + 9.8(x-5) So, we match their heights and we get 427...

*September 27, 2016*

**Math**

v^2 = 2as 35^2 = 2a*18 a = 34 m/s^2 You have no idea how long it took to accelerate. The units in your calculation are all jumbled up.

*September 27, 2016*

**math**

8/x + 3/4 < 2 8/x < 5/4 now you can easily find x.

*September 27, 2016*

**math**

set x=0: 0 + 4y = 15

*September 27, 2016*

**Math**

first, find the common denominator for each problem. Then you can work with the fractions more easily.

*September 27, 2016*

**Engineering Math**

well, apparently P(a-bP) = bP(300 − P) aP - bP^2 = 300bP - bP^2 so, a = 300b dP/dt = P(300b-bP) = bP(300-P) Try plugging that in. You already know what the logistic growth function looks like, so that should guide your efforts some.

*September 27, 2016*

**maths need help**

If there are n terms, we have a + ar = x ar^(n-2) + ar^(n-1) = y a(1+r) = x ar^(n-2)(1+r) = y now divide r^(n-2) = y/x r = (y/x)^(n-2)

*September 27, 2016*

**maths trig need help**

clearly not true at x = pi/4. The LS is undefined while the RS = √2.

*September 27, 2016*

**math**

3x - 1(19-x) >= 32

*September 27, 2016*

**physics**

h = (v sinθ)^2 / 2g

*September 27, 2016*

**Algebra**

there are lots of linear regression calculators online, such as http://ncalculators.com/statistics/linear-regression-calculator.htm

*September 27, 2016*

**further maths**

you can start by dividing by 5 everywhere 5x-30x+25=0

*September 27, 2016*

**Math**

7^{-10}

*September 27, 2016*

**physics**

°C = 5/9 (°F-32) now just plug in F=1800

*September 27, 2016*

**physics**

no "fever" 37°C = 98.6°F

*September 27, 2016*

**maths**

if the last digit is 4, then there are 6! ways If the last digit is 2 or 8, then there are only 6!/2! ways because of the duplicate 4s. So, there are only 2*6! total ways

*September 27, 2016*

**Urgent Math**

First, do a long division x^3/(x^2+1) = x - x/(x^2+1) for the 2nd term, let u=x^2+1

*September 27, 2016*

**Math**

either 2x+50 = 180 or 2*50+x = 180

*September 27, 2016*

**Math**

Let u=18x-x^2-77 log_3(u) exists if u>0 log_5(log_3)u)) exists if log_3(u)>0, or u > 1 log_4(log_5(log_3(u))) exists if log_5(log_3(u)) > 0, or log_3(u) > 1, or u > 3 So, we need 18x-x^2-77 > 3 18x-x^2-80 > 0 (10-x)(x-8) > 0 8 < x < 10

*September 27, 2016*

**math**

After 20 min. there will be 2^20 bacteria

*September 27, 2016*

**Further mathematics**

Draw a triangle with adj. side L hypotenuse 1 opp. side: √(1-L^2) Now you can just read off the other trig functions and use them in your expression.

*September 27, 2016*

**pre-calculus**

I'm sure if you review the properties of ellipses you can come up with the values given at http://www.wolframalpha.com/input/?i=ellipse+(x%2B3)%5E2%2F24+%2B+(y-5)%5E2%2F49%3D1

*September 27, 2016*

**math**

uh, 5% more, right?

*September 27, 2016*

**college trip**

a) 2 rev/hr = 4π rad/hr b) 4π*125 ft/hr now make that into mi/hr

*September 26, 2016*

**Math**

I get 2+(2+1) + 3+(3+1) add each number to "itself plus one"

*September 26, 2016*

**Math**

surely you can add. ?

*September 26, 2016*

**Math**

the circumference of a circle with radius 21"

*September 26, 2016*

**calculus help plllllz**

wow Just looking at the answer at http://www.wolframalpha.com/input/?i=%E2%88%AB%5B%7B(1-sin(x))%2F(1%2Bsin(x))%7D%7B(2-sin(x))%2F(2%2Bsin(x))%7D%5D+dx I'd start with u = sinx dx = 1/√(1-u^2) du Then you are dealing with (1-u)(2-u) -------------- * 1/√(1-u^2) ...

*September 26, 2016*

**Math**

Well, if you got the question wrong, there's little hope of getting the right answer. You have not made it clear how we decide which student gets which souvenir when.

*September 26, 2016*

**Math**

A is right a limit of infinity means it does not exist.

*September 26, 2016*

**Ortiz**

how long does it take each car to go 500m? A: t = 500m/(40 m/s) B: 5t^2 = 500

*September 26, 2016*

**Maths**

the diameter of the hemisphere is the same as the base of the cone. So, add up a cone and half of a sphere. I trust that you have those formulas handy. Just plug in your numbers.

*September 26, 2016*

**Physics**

using similar triangles, you can see that after flying the full 394 km, the plane would be 394/203 * 17.5 = 34 km west of city B. So, in the diagram, let P = place where the plane would end up after 394km Draw a line east from P to intersect AB at Q, and the line north from A ...

*September 26, 2016*

**Algebra 2**

oh. well, then change the formula and solve for n.

*September 26, 2016*

**Algebra 2**

On the nth bounce it rises to a height of 25 * 0.45^n so, solve for n in 25*.45^n = 10.24 You sure there's no typo? 25*.45 = 11.25 11.25*.45 = 5.06

*September 26, 2016*

**Math**

negative infinity is the correct answer. That means the limit does not exist.

*September 26, 2016*

**math**

1/45 + 2/45 = 1/x

*September 26, 2016*

**Math**

since the horizontal axis is weeks, that is usually the independent variable. So, I'd say the graph represents how many days are in a given number of weeks. days = 7*weeks

*September 26, 2016*

**Intermediate algebra**

you have something against the digit 0? Why drag in the Greek letter phi? Assuming you want to find vales of x which make the equation true, you have three choices: 8=0 x = 0 x-1 = 0 I guess you can find the needed x values now, right? The reason we always set the product on ...

*September 26, 2016*

**math**

sure 100*1 = 100 999*9 = 8991 So, most of the values in between will be the product of a 3-digit number and a 1-digit number.

*September 26, 2016*

**Math**

well, 4840 ft^2 is 1/9 acre Not sure why you dragged that in, nor even why you care about ft^2 when the discussion is involving fractions of acres.

*September 26, 2016*

**Math**

it would depend on the speed of the dive. I suspect that most dives do not take hours.

*September 26, 2016*

**Functions**

if there is no value of y for some x, then it is not even a relation, much less a function. There must be exactly one y for each x.

*September 26, 2016*

**Functions**

easy. All polynomials are functions. each value of x produces a single value of y. This assuming I am correctly interpreting what you mean by a "polynomial equation."

*September 26, 2016*

**maths quartic equation need help**

since the polynomial has real coefficients, complex roots must come in conjugate pairs. SO, it has another root of 1-2i (x-(1+2i))(x-(1-2i)) = ((x-1)-2i)((x-1)+2i) = ((x-1)^2 - (2i)^2) = x^2-2x+5 Now divide the quartic by that, and you will be left with another quadratic, ...

*September 26, 2016*

**Algebra**

1B ok 2B 6-2=4, not 6/2 = 3 Just as in #1 you added powers when multiplying, you subtract powers when dividing. 3D 5^-3 = 1/5^3 = 1/125 You just dis 1/(5*3) 4B Think of division, and subtracting powers: 5^3/5^3 = 5^(3-3) = 5^0 x^0 = 1 for any nonzero value of x. 5A,B,D Not E, ...

*September 26, 2016*

**calculus help me pllllllllllz**

If you follow the threads of that web site, you will probably see how wolframalpha came up with its soution: http://www.wolframalpha.com/input/?i=%E2%88%AB%5B0,infinity%5D+dx%2F(x%5E4%2B4)

*September 26, 2016*

**calculus help me pllllllllllz**

Oh. I'm sorry. I misread the integral. x^4+4 is a bit trickier. But, as usual, google turned up several discussions. You might care to start here: http://www.freemathhelp.com/forum/threads/55678-difficult-integration-int-1-(1-x-4)-dx

*September 26, 2016*

**calculus help me pllllllllllz**

let x = 2tanθ x^2+4 = 4tan^2θ+4 = 4sec^2θ dx = 2sec^2θ dθ now the integrand becomes 2sec^2θ/4sec^2θ dθ = 1/2 dθ Now recall that tan(π/2) = ∞ This is just a reminder of one of the standard forms: ∫ dx/(x^2+a^2) = 1/a...

*September 26, 2016*

**algebra**

14/15 + 1/5 = 17/15

*September 26, 2016*