Sunday

December 21, 2014

December 21, 2014

Total # Posts: 27,657

**calculus**

f is decreasing when f' is negative and similarly for increasing f is concave down when f" is negative and similarly for concave up f = 3 + 4xe^-5x f' = 4(1-5x)e^-5x f" = 20(5x-2)e^-5x Hint: e^-5x is never zero
*October 17, 2014*

**calculus**

not sure what is the difference between an and {an} Do you mean |an|?
*October 17, 2014*

**calculus**

review your 1st and 2nd derivative meanings f' = -6(1+sinx)cosx f" = 6(sinx-cos(2x))
*October 17, 2014*

**Algebra**

Not sure what operation @ indicates. Now what all the ? signs are supposed to mean. Clearly the domain is the set of values of x for which f(x) is defined. There appears to be a change of definition in the domain. Is f(x) the same on both sides of that point? ow about using ...
*October 17, 2014*

**math**

since time = distance/speed, 8/s + 8/(s+15) = 2 So the speeds were 5 and 20 mi/hr
*October 17, 2014*

**Calculus**

well, that would be when p' = 0. So, p' = 50(-e^-x + 2xe^-x^2) You can use your favorite graphing utility or numerical method to find where p'(x) = 0. The graph of p(x) is at http://www.wolframalpha.com/input/?i=50%28e^-x+-+e^-x^2%29%2B10+for+0%3C%3Dx%3C%3D2 If you...
*October 16, 2014*

**math**

No idea. Just start listing them, fewest coins first. Then start breaking down into smaller values 50 10 50 5 5 50 5 1 1 1 1 1 50 1 1 1 1 1 1 1 1 1 1 25 25 10 ...
*October 16, 2014*

**Calculus**

you want to find where p'(x) has a max p' = 50(2x e^-x^2 - e^-x) See http://www.wolframalpha.com/input/?i=2x+e^-x^2+-+e^-x
*October 16, 2014*

**Calculus..**

you want where s' is the same for both particles -4sin(4x) = x^2-x+2 Better use a graphing utility of numeric method. See http://www.wolframalpha.com/input/?i=-4sin%284x%29+%3D+x^2-x%2B2
*October 16, 2014*

**math**

you will have factors of 5,10,15,20,25,30,35,40,45,50 which means you will have 5^12 There will be many more multiples of 2, so 10^12 will be a factor Looks like 12 zeros
*October 16, 2014*

**Algebra2**

powers of i cycle through. i^0 = 1 i^1 = i i^2 = -1 i^3 = -1 i^4 = 1 and so on. i^100 = (i^4)^25 = 1^25 = 1 I can't figure out what you're asking on the first part.
*October 16, 2014*

**AP Calculus**

think of a rectangle. The rectangle with the largest area is a square. So, 30^2 = 900 Any other two numbers with sum=60 will have a smaller product. They will be (30-k) and (30+k), whose product is 30^2 - k^2
*October 16, 2014*

**AP Calculus**

If we have base x^2 and height y, 2x^2 + 4xy = 600 v = x^2y = x^2(600-2x^2)/4x = 150x - x^3/2 Now just find x where v' = 0
*October 16, 2014*

**math**

If all we are interested in is the number of shares, all the info about their value is just noise. a+b = T a=79 79+b = T b = T-79 a = T-b b = T-a and so on
*October 16, 2014*

**Math**

the list must have pairs, working in from the ends. The only such lists I see are C and D
*October 16, 2014*

**math**

the definition of π is the ratio of the circumference to the diameter of a circle. So, C/d = π The diameter is twice the radius So, C/2r = π C/r = 2π
*October 16, 2014*

**Algebra**

between the two, they cover the 230 ft. So, after Belle has been swimming x seconds, 2x + 5(x-10) = 230 2x + 5x - 50 = 230 7x = 280 x = 40
*October 16, 2014*

**math**

Looks unchanged to me. Still A'B
*October 16, 2014*

**Algebra**

this is another just like the others. The relative speed of the 2nd car is 10 km/hr faster. In two hours, the 1st car has gone 60km. So, it takes 6 hrs for the 2nd car to catch up. By that time, the 1st car has been going for 8 hours. Or, as Reiny showed you, you want to find ...
*October 16, 2014*

**Math**

your inequality is correct. So, 750+35w > 1200 35w > 450 w > 12.8 Since she probably doesn't get paid till the end of the week, that means she'll need to work at least 13 more weeks to have the $1200 saved up.
*October 16, 2014*

**Math algebra Help please**

so the area is increased by a factor of 6^2
*October 16, 2014*

**Math**

Where's the product. You should have said (2+(n/3))*(a-4) I can see where it might also be (2+n)/3 * (n-4) That assumes that the two numbers are the same. If not, it'd be (2+a)/3 * (b-4)
*October 16, 2014*

**Algebra**

the trains are separating at 70+50=120 mi/hr When the 2nd train left, they were already 50 miles apart. So, the remaining 300 miles will take 300/120 hours. Add that to the original hour head-start.
*October 16, 2014*

**Science**

which disorder?
*October 16, 2014*

**Math**

where did you get the 4? the quotient of a and b is a/b. So, you have the quotient of 2 and the sum of a number and 5 2/(x+5)
*October 16, 2014*

**science**

the event is indeed the formation of the rock. From that point on, the strontium in the rock decays, allowing determination of the age of the rock.
*October 16, 2014*

**Physics**

Magnetic field = permeability x turn density x current For a solenoid of length L =0.745m with N =350 turns, the turn density is n=N/L turns/m. If the current in the solenoid is I =1.69 amperes and the relative permeability of the core is k =1( air) then the magnetic field at ...
*October 16, 2014*

**Math**

n = 2d-1 5n+10d = 855 now crunch the numbers.
*October 16, 2014*

**Algebra**

the real problem, as I see it, is that you don't know the formula. How can you be given a problem about perimeters and not have learned how the perimeter is figured?
*October 16, 2014*

**Algebra**

you know the perimeter is 2(width + length) So, now you are told that l = 3w and that 2((l+4)+(w-1)) = 102 since l=3w, that means 2((3w+4)+(w-1)) = 102 3w+4+w-1 = 51 4w+3 = 51 4w = 48 w = 12 Now you can figure the original length.
*October 16, 2014*

**Algebra**

2((3w+4)+(w-1)) = 102 w=12 2((2x+6)+(3x-1))) = 90 x=8 So, on both problems, you can now figure the answers needed.
*October 16, 2014*

**Calculus**

I find it a lot more readable just to use y', instead of all those dy/dx. And, there's no reason to rearrange the equation. arctan(x^5y)=xy^5 1/(1+x^10y^2) (5x^4 + x^5y') = y^5 + 5xy^4y' 5x^4y/(1+x^10y^2) + x^5y'/(1+x^10y^2) = y^5 + 5xy^4y' Now collect ...
*October 16, 2014*

**Algebra**

a = 2g-6 5a = 8g Now just solve for a.
*October 16, 2014*

**Math**

well, it's clear that cosθ = -1/2 There will be solutions in QII and QIII
*October 16, 2014*

**Pre-Calc/Trig...**

you know that if the product is zero, one of the factors must be zero. SO, you have x-3 = 0 or x+2 = 0 The solutions are therefore x = -2 or x = 3. I assume you can now pick the solution with the lower value. Don't forget your algebra I, now that you're taking pre-calc!
*October 16, 2014*

**Math**

cosθ = -1/2 solutions in QII and QIII
*October 16, 2014*

**Trigonometry**

remember your double-angle formula tan2A = 2tanA/(1-tan^2 A) so, 2tanA/(1-tan^2 A) - 2tanA = -1 2tanA * tan^2 A = tan^2 A - 1 2tan^3 A - tan^2 A + 1 = 0 Hmmm. Nasty. You need to solve 2x^3 - x^2 + 1 = 0 and then take the arctan of whatever solution you find.
*October 16, 2014*

**math**

Since B+D-(B&D) = 320, 300 + D - 280 = 320 D = 300 300-280 = 20 buy only DVDs. Or, you can reason that if 300 bought Blu-ray, and 280 of those also bought DVD, then only 20 bought just Blu-ray. So, That means that the remaining 20 bought only DVDs
*October 16, 2014*

**Advanced math**

since 1,1,1,1,1... has its function ∞ ∑x^n = 1/(1-x) n=0 take the derivative ∑nx^(n-1) = 1/(1-x)^2 now replace n-1 with n and you have ∑(n+1)x^n = 1/(1-x)^2 generates 1,2,3,4,5,...
*October 16, 2014*

**Math**

well, you know the solutions will all be in QI and QIV and you know cosθ = 1/2
*October 16, 2014*

**Advanced math**

Take a look here: http://math.stackexchange.com/questions/54961/the-number-of-partitions-of-n-into-distinct-parts-equals-the-number-of-partiti and I think you will see how to build the proof you want.
*October 16, 2014*

**Programming**

print "mileage at start" read milesout print "mileage at end" read milesin print "liters consumed" read fuel rate = (milesin-milesout)/fuel print "fuel consumtion rate: ",rate," miles/liter" Now go code it up and adjust the ...
*October 16, 2014*

**Math**

check the ratio of successive terms. If it's constant, you have a GP (4x-2)/2x =?= (6x-4)/(4x-2) (2x+2)/(x+1) =?= (5x+1)/(2x+2) Looks like neither to me.
*October 15, 2014*

**math**

3√45x-√27x+17√3x-9√125x^3 3*3√5x - 3√3x+17√3x-9*5x√5x -36√5x + 14√3x or, if you will, 2√x (7√3-18√5)
*October 15, 2014*

**8th grade**

If cost = revenue for x cameras, then 2050+7x = 17x x=205 Assuming you mean 50 more than the break-even number, then since profit = revenue - cost, p = 17*255 - (2050+7*255) Another way to look at it is that the profit per camera is 17-7=10 dollars. So, with zero profit at 205...
*October 15, 2014*

**Algebra Help**

since you have 2x^2, the parabola opens upward So, it must have a minimum, which occurs at x = -16/4
*October 15, 2014*

**Math**

you are correct.
*October 15, 2014*

**Trigonometry**

I'd do it like this: in QII if sinA = 12/13, cosA = -5/13 in QIV, if sinB = -7/25, cosB = 24/25 So, tanA = -12/5 tanB = -7/24 tan(A-B) = ((-12/5)-(-7/24))/(1+(-12/5)(-7/24)) = (-253/120) / (204/120) = -253/204
*October 15, 2014*

**Math**

see a similar problem at http://www.jiskha.com/display.cgi?id=1413396134
*October 15, 2014*

**calculus**

For the graph, see http://www.wolframalpha.com/input/?i=+r+%3D+2sin%5E2%CE%B8 For the area, recall that in polar coordinates, a = ∫∫ r dr dθ = ∫[0,2π] ∫[0,2sin^2θ] r dr dθ = ∫[0,2π] 1/2 r^2 dθ [[0,2sin^2θ] = &#...
*October 15, 2014*

**algebra**

You will need x lbs, where the ratio of lbs/people remains the same. That is, 3/8 = x/10 30 = 8x x = 15/4 = 3 3/4 lbs Oh, and you'll also need a larger pie pan...
*October 15, 2014*

**Argebra 2**

enough for the anticipated pies, I guess. Sure there's not something more you want to tell us? Like how many lbs it takes to make a pie? Or how many cups, or something? If you really don't know any more than this, better look online for recipes, and they'll tell ...
*October 15, 2014*

**Pre-Calc/Trig...**

x^2 (x-2)^2 shift right 2 5(x-2)^2 stretch vertically by 5 5(x-2)^2+1 shift up 1 That should help decide.
*October 15, 2014*

**Calculus problem (PLEASE HELP!!)**

try multiplying top and bottom by x^0.3 (2x^0.3+4)/(x^0.3+1) Now you have a nice simple limit of 4/1 As x gets big, x^-0.3 vanishes, and the limit is 2/1
*October 15, 2014*

**Map to sacle**

well, if it were a scale of 1:2, it'd be 1/2 as big, right? So, you can see it will be 420/8000 m Now I'd suggest you convert that to cm for easier visulatization.
*October 15, 2014*

**Calculus (Need help)**

for f to be continuous, all three definitions must be equal at x=1. Since f is defined at x=1 in three different ways, we need -3a+4b = a-2b-1 a-2b-1 = 3-b+a So just solve those for a and b
*October 15, 2014*

**math**

Since you mention the length of the car and truck, I assume that you want the rear of the car to pass the front of the truck. So, the rear of the car is 3+10+10=23 m from the front of the truck. At a relative speed of 50 km/hr, that will take 23m/(50km/hr * 1000m/km) = 23/...
*October 15, 2014*

**math**

35 in to the square root of 2 ? Do you mean 35 in^2 If so, that's the power 2, not to the √2 Anyway, that's not enough information. Even if you restrict the rectangle to integer dimensions, it could be 1x35 - perimeter=72 5x7 - perimeter=24
*October 15, 2014*

**Geometry**

I guess C is the midpoint of AD. if so, then 5x-8 = 16-3x x = 3 Now you can find the lengths. If not, then you need to provide more details.
*October 14, 2014*

**math**

1/k + 1/7 = 1/4 Now just solve for k.
*October 14, 2014*

**Geometry**

Many people use m<A to mean "measure of angle A" Also <= or >= for less/greater than or equal
*October 14, 2014*

**Geometry**

interior is 180-x # sides is 360/x
*October 14, 2014*

**Pre-Calc/Trig...**

nope. No shapes get deformed or warped, or scaled. The whole rigid system is just moved upward.
*October 14, 2014*

**Math**

A is in QII, so cosA = -5/13 B is in QIV, so cosB = 24/25 Now, you have cos(A-B) = cosAcosB + sinAsinB ...
*October 14, 2014*

**Chemsitry**

How many grams of ice at -24.3∘C can be completely converted to liquid at 23.9∘C if the available heat for this process is 4.82×103kJ ? For ice, use a specific heat of 2.01J/(g⋅∘C) and ΔHfus=6.01kJ/mol.
*October 14, 2014*

**Foundations and Pre-Calculus Math 10**

v = 1/3 pi r^2 h so, pi/3 r^2 (3) = 30 r^2 = 30/pi r = ...
*October 14, 2014*

**Pre-Calc/Trig...**

both correct
*October 14, 2014*

**Perimeter and Area**

did you plot the points? The first one is clearly a square. So, now what is your choice? The second, assuming no typos, has duplicate points, so it is just a short vertical line.
*October 14, 2014*

**math**

Since the vertex is set at (0,0), you have a parabola y = ax^2 where y(200) = 100 a*40000 = 100 a = 1/400 y = 1/400 x^2
*October 14, 2014*

**Math**

1 kg = 1000g 603kg = 603*1000 g
*October 14, 2014*

**Math**

clearly a cube with side equal to the diameter of the sphere. So, since for a sphere, v = pi/6 d^3, just plug in your numbers and solve for d.
*October 14, 2014*

**Math 116**

since a=lw, your new area is (1.1l)(0.9w) = 0.99 lw So the area has decreased by 1%
*October 14, 2014*

**Math 130**

sure you can find the desired measures. Just consult your text for the relevant formulas and examples.
*October 14, 2014*

**Math**

Extend the sides to meet at point E. Since each exterior angle is 60°, angle BCE = CBE = 60° So, now you only have to find the third angle (angle E) of triangle BCE.
*October 14, 2014*

**c programming**

wow. Things would have been have been a lot more compact if you had used an array of month days: modays[12] = [0,31,28,31,30,...] and then just adjusted the 28 as needed for the leap year.
*October 14, 2014*

**math**

1/2 < x/8 multiply by 8 on both sides: 4 < x
*October 14, 2014*

**Algebra**

If there are x 4-seaters, and y 10-seaters, then x+y <= 52 4x + 10y >= 280 see the solution set at http://www.wolframalpha.com/input/?i=solve+x%2By+%3C%3D+52%2C+4x+%2B+10y+%3E%3D+280%2C+x%3E%3D0%2C+y%3E%3D0
*October 13, 2014*

**math**

since each equation is a straight line, each has exactly one solution. Think on it. A solution is where the graph intersects the x-axis. Two distinct lines intersect in exactly one point, unless they are parallel.
*October 13, 2014*

**pre-calculus**

revenue is room-charge * #rooms, so R(x) = (700+14x)(550-7x) That's just a parabola, and you can easily find its vertex.
*October 13, 2014*

**Algebra**

well, duh: 15 + .5x = 25 + .25x Now just solve for x...
*October 13, 2014*

**Math**

well, you have the formula: v = (3+2i)(4-i) = 14+5i
*October 13, 2014*

**Algebra**

Start from 110 feet away, a person on a bicycle rides toward a checkpoint a nd then passes it. The rider is traveling at a constant of 30m feet per second. The distance between the bicycle and the checkpoint is given by the equation d=(110-30t). At what times is the bike 40 ...
*October 13, 2014*

**Algebra 2**

If we call the equations #1,2,3 then subtract #1 from #2 and #3 from #3 to get 96a + 8b = 2 84a + 6b = 0 So, 6b = -84a, meaning 8b = -112a So, 96a - 112a = 2 -16a = 2 a = -1/8 now use that to get b = 7/4 c = 7 It would have been nice for you to have shown your work. Oh well, ...
*October 13, 2014*

**College Physics**

Since all her KE is converted to PE, 1/2 mv^2 = mgh so, 1/2 * 39.7^2 = 9.81h Note that the angle of incline makes no difference.
*October 13, 2014*

**Algebra help**

If you mean to say f(x) = 5x-1, then you are correct.
*October 13, 2014*

**Math**

as was already posted, 2cos^2 θ
*October 13, 2014*

**Intro to Programming PT1420**

nothing - there is a syntax error.
*October 13, 2014*

**Math**

If the intensity on Earth is x, then since Id^2 = k is constant, 9140*.387^2 = 1x As for rate of change, who says it's changing?
*October 13, 2014*

**Math**

Yes, I can.
*October 13, 2014*

**Physics**

If she has mass m, then she is part of the total mass. So 120 = (8.4+m)(1.7) Now just solve for m.
*October 13, 2014*

**physics please help**

√(4.57^2 + 4.74^2) / 5.76 = 1.14 m/s^2 I expect you can figure the direction.
*October 13, 2014*

**vp manthata secondary school**

Since v = πr^2h 42 = 5πr^2 r^2 = 42/(5π) r = √(42/(5π))
*October 13, 2014*

**College Math**

(a) a circle always gives the largest area for a given perimeter. Among rectangles, a square gives the largest area. (b) 1: p = 120/4 = 30 ft area: 7.5^2 = 56.25 2: c = 120/5 = 24 area: = 45.8 So, the expensive fencing reduces the circular area for planting.
*October 13, 2014*

**MATH 101**

15x^2(2x + 3) + 41x(2x + 3) + 28(2x + 3) (15x^2+41x+28)(2x+3) (3x+4)(5x+7)(2x+3)
*October 13, 2014*

**MATH 101**

40(30+41t+7t^2) 40(5+t)(6+7t)
*October 13, 2014*

**math**

(10+4)(6+4)-(10)(6)
*October 13, 2014*

**Math**

(4/5)(m-m/12) = 704 (4/5)(11/12)m = 704 11/15 m = 704 m = 704 * 15/11 m = 960
*October 13, 2014*

**Math**

After taxes, a $1 items sells for $1.085 So, the items sold account for all the extra money: (1065.95-122.00)/1.085 = 870 That's how many items were sold.
*October 13, 2014*

**Math-Urgent help please.**

4/52 * 4/51 = 0.00603 so, knowing that, choose 2
*October 13, 2014*

**Kennedy king**

(1+r)^10 = 2.0 1+r = 2.0^0.1 r = 2.0^0.1 - 1 So, to grow by a factor of 1.5, will take (1+r)^t = 1.5 2^.1t = 1.5 .1t = log1.5/log2 t = 10(log1.5/log2) = 5.85 years Depending on when interest is posted, it could take up to 6 years to see the $15K
*October 12, 2014*

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