Monday

January 26, 2015

January 26, 2015

Total # Posts: 28,353

**Algebra 1**

Write y= -2/3x +7 in standard form using integers.
*December 16, 2014*

**Calculus**

Hmmm. As I recall, the average value of f(x) on [a,b] is ∫[a,b] f(x) dx ------------------ b-a e^(4x^2) is an even function, so its average value cannot be zero over [-1/4,1/4]. ∫[-1/4,1/4] e^(4x^2) dx Unfortunately, ∫e^(x^2) dx is not an elementary integral.
*December 16, 2014*

**Algebra 1**

thank you
*December 16, 2014*

**Algebra 1**

Write an equation in point slope form for the line through the given point with the given slope. (4,-7); m= -0.54
*December 16, 2014*

**calculus**

no, s(t) is the position function. You want the velocity, which is ds/dt = -9.8t then you can sub in t=3. And, since the ball is falling, s(t) = -4.9t^2 + 550
*December 16, 2014*

**Trig/Precalc**

Yes, there are lots of such formulas. One is at http://www.uwfox.uwc.edu/users/tnyman/TRIGConcepts/Asinx+Bcosx.pdf where you will see that the amplitude of your function is √(5^2+6^2) = √61
*December 16, 2014*

**Algebra 2**

ax+by=c ax=c-by x = (c-by)/a
*December 16, 2014*

**math**

Mr jacob is 55 years old and Tony is 7 years old. In how many years will Mr. Jacob be 4 times as old as Tony?
*December 16, 2014*

**math**

The cost of 5 similar digital cameras and 3 similar video cameras is $3213. each video camera costs 4 times as much as each digital camera. John buys a digital camera and a video camera. How much does he pay?
*December 16, 2014*

**math**

Three times as many children as adults attended a concert on Saturday. An adult's ticket cost $7 and child's ticket cost $3. the theater collected a total of $6,000. How many people bought tickets?
*December 16, 2014*

**English - Writeteacher**

Your choices look good to me.
*December 16, 2014*

**math**

(4/56)*42 Or, you can write that as x/42 = 4/56
*December 16, 2014*

**Chemistry**

I think that the crystal lattice has little to do with it at this point. By saying that the Al atom has a volume, they just want you to divide the mass of an atom by its volume. Without more information on the lattice spacings in 3D, it's hard to say how much space an atom...
*December 16, 2014*

**MATH**

1/(6 4/5) * 30
*December 16, 2014*

**Math One question! Help!**

The rate of change is the slope of the line. The slope-intercept form of this line is y = -5/3 x - 2/3
*December 16, 2014*

**Algebra 2**

to evaluate c, just plug in x(t) wherever there's an x: c(x(t)) = 60x(t)+750 = 60(50t)+750 = 3000t+750 Now just plug in t=5 to get c(x(5)).
*December 16, 2014*

**English**

Looks to me like STAY is intransitive ASKED is transitive, since it has an object.
*December 16, 2014*

**physics**

v = at where a is just the acceleration due to gravity. So, solve for t in 9.8t = 85(1000/3600)
*December 16, 2014*

**Math**

wherever you see an x, place a -7. So, f(-7) = -(-7)-6 = 7-6 = 1
*December 16, 2014*

**Math**

well, there's 1* log + 1/2 * log Looks like 3/2 * log to me... Do you have trouble with x + 1/2 x = 3/2 x?
*December 16, 2014*

**Math**

2 = (1/2)^-1, so log(1/2)2 = -1 log(1/2)2 + log(1/2)2^(1/2) log(1/2)2 + (1/2)*log(1/2)2 (3/2)*log(1/2)2 (3/2)(-1) -3/2
*December 16, 2014*

**calculus**

If the base of the ladder is x away from the wall, and the top of the ladder is at height y, then x^2+y^2 = 25^2 x dx/dt + y dy/dt = 0 So, figure y when x=20, and plug in dx/dt=0.18 to find dy/dt.
*December 16, 2014*

**Math**

reflection over the x-axis takes (x,y) -> (x,-y) So, just change the sign of all the y-coordinates in your points.
*December 16, 2014*

**algebra**

The fundamental theorem of algebra says that every polynomial of degree n has exactly n roots. So, look at the highest power of the variable.
*December 16, 2014*

**maths**

99... still working on the ending digit(s)
*December 16, 2014*

**MATH**

The answer is clearly 5, because you have to include the 3 the person ate!
*December 16, 2014*

**Math**

just google it. You will find many proofs of it.
*December 16, 2014*

**Math - incomplete**

how many partitions? Is the fence used to separate the partitions? And what do you want x to represent?
*December 16, 2014*

**math**

You need to divide the region into two parts at x=1, where 3x and 5-2x intersect. a = ∫[0,1] (3x - x/2) dx + ∫[1,2] (5-2x - x/2) dx See the region at http://www.wolframalpha.com/input/?i=plot+y%3D3x%2Cy%3Dx%2F2%2Cy%3D5-2x
*December 16, 2014*

**math**

s = ∫[0,5] √(1+y'^2) dx = ∫[0,5] √(1+9x/4) dx That will give the length of one branch of the curve.
*December 16, 2014*

**chem**

NaH2PO4 Molecular Weight 119.98 I guess that's about as close as you're gonna get. But I guess you can use google as well as I can...
*December 16, 2014*

**MATHS**

n = 2d-4 (n+1)/(d+1) = 3/2 (2d-4+1)/(d+1) = 3/2 2(2d-3) = 3(d+1) 4d-6 = 3d+3 d = 9 So, the original fraction is 14/9
*December 16, 2014*

**Chemistry**

Hmmm. Which of those devices do you know has an antenna?
*December 16, 2014*

**basic chemistry**

you need the balanced equation: 2Na3PO4 + 3BaCl2 --> Ba3(PO4)2 + 6NaCl So, each 2 moles of Na3PO4 yields 1 mole of Ba3(PO4)2
*December 15, 2014*

**Physics**

clearly, since they are all on the same rigid platform, their rotational periods are all the same. Since the circumference is just a constant times the radius, their speeds are in the same proportion as their radii. Someone 1/2 as far out is going 1/2 as fast. since the radial...
*December 15, 2014*

**Algebra 3**

you just need to remember that the vertex of the parabola y = ax^2+bx+c occurs at x = -b/2a.
*December 15, 2014*

**pre algebra**

You are correct as far as you got. By the time the police get started, the robbers are 13 miles ahead. The police are going 60 mi/hr faster than the crooks. So, you can think of the problem as the same thing as the robbers are standing still 13 miles ahead, and the police are ...
*December 15, 2014*

**Calculus**

if you let u = 1 + (x-3)^2 then y = 1/u The chain rule says that y' = -1/u^2 u' = -1/(1+(x-3)^2)^2 * (2(x-3))
*December 15, 2014*

**Algebra 1**

Thank you
*December 15, 2014*

**Algebra 1**

what is the equation to y= -1/12x+4 so that the 2nd line is parallel?
*December 15, 2014*

**Quick math help**

can't you see how incomplete your explanation is? Read that paragraph to anyone not familiar with the diagrams and they will blankly say, "Huh? what triangles?"
*December 15, 2014*

**math**

If the boat's speed is b and the current's speed is c, then since distance = speed * time, 10(b+c) = 210 70(b-c) = 210 Now just solve for b and s.
*December 15, 2014*

**Math**

a1+...+a9 = 5a + (0+2+4+6+8)d a2+...+a10 = 5a + (1+3+5+7+9)d so, 5a+20d = 17 5a+25d = 15 d = -2/5 a = 5
*December 15, 2014*

**Math Plz dont ignore Plz**

You just need to read through the words and write down the mathematical facts. They want to know how many adults and children were admitted. So, let's say there are a adults and c children. 1850 adults and children means a+c = 1850 $4.50 per child and $7.50 per adult and ...
*December 15, 2014*

**AP Calc BC**

y' = √x / -3y -3y dy = √x dx -3/2 y^2 = 2/3 x^(3/2) + c so, yes, you are correct y^2 = -4/9 x^(3/2) + c Not much to do with that. I guess you could use a new c. Name the old one k and you have y^2 = k - 4/9 x^(3/2) If k = 4/9 c then y^2 = 4/9 c - 4/9 x^(3/2) y...
*December 15, 2014*

**AP Calc B/C**

So, add up all the little wafers with diameter x^3, perpendicular to the x-y plane. They would have their centers at (x,y/2) with radius y/2 = x^3/2. The volume of a small semi-circular wafer of radius r and thickness dx is 1/2 πr^2 dx v = ∫[0,4] 1/2 π(x^3/2)^2...
*December 15, 2014*

**math**

well, since 27 = 4*6 + 3 what do you think?
*December 15, 2014*

**Math**

1/3 + √3/12 + 1/16 + √3/64 Using a common denominator of 64*3, we have (64 + 16√3 + 12 + 3√3)/192 (76+19√3)/192 or 19(4+√3)/192
*December 15, 2014*

**MATH**

-1+6 = 5, so -5(5) = ?
*December 15, 2014*

**math**

B:H = 4:7 H:J = 3:5 7*3 = 21, so we also have B:H = 12:21 H:J = 21:35 So, B:H:J = 12:21:35 12+21+35 = 68 136/68 = 2, so double everything so the sum is 136 B:H:J = 24:42:70 and those are the amounts for each girl.
*December 15, 2014*

**Algebra 1**

10.5^2
*December 15, 2014*

**Algebra 1 thx**

Does the coach count as one round? If so, the nth round has 3^n calls. If not, then the nth round has 3*3^n calls
*December 15, 2014*

**Algebra please help answer**

40/10 = 4, so it will triple 4 times. 3^4 = 81
*December 15, 2014*

**math**

If the cost is the same for x hours, then clearly 200+30x = 240+25x
*December 15, 2014*

**calc**

the tangent vector is ∇v = (dx/dt,dy/dt,dz/dt) ∇v = <4∛t,6t,-4/t^3> v(-1) = <3,-3,2>, so ∇v = <-4,6,4> Note that <-2,3,2> is parallel to ∇v(-1)
*December 15, 2014*

**math**

x=175, if that's what you are after
*December 15, 2014*

**Math**

since the ratio of the sides remains the same, x/5 = 5.1/3
*December 15, 2014*

**CAL**

y = 4/9 sinx - 1 y' = 4/9 cosx So, the slope of the tangent at x is 4/9 cosx The slope of the normal there is -1/y' = -1/(4/9 cosx) = -9/4 secx
*December 15, 2014*

**Math**

5000-7 = 4993 4993 = 5*998 + 3 7+4990 = 4997 The next number would have been 5002 Or, using modulo 5 math, 7 = 2(mod 5) 5000 = 0(mod 5) So, 5002 = 2 (mod 5)
*December 15, 2014*

**Math**

If the sequences are P and T, and their differences are Pd and Td, then T1 = -P1 2013/2 (2T1+2012Td) = 2013/2 (2P1 + 2012Pd) or, 2013P1 + 2025078Pd = 2013T1 + 2025078Td 4026P1 + 2025078(Pd-Td) = 0 We know that since T1 < 0 and the sum of T is the same as the sum of P, that ...
*December 15, 2014*

**calculus**

There must be problems on extrema. The extrema occur where f' = 0. Here, f(x) = x^(1/3) f'(x) = 1/3 x^(-2/3) f'(x) is never zero anywhere, especially in this interval. So, we just want the maximum and minimum values attained on the interval. Note that f' > 0...
*December 15, 2014*

**Algebra 1**

What is an equation of the line with slope 6 and y intercept -4?
*December 15, 2014*

**Math**

For all the garden subdivisions, 2 of 3 sections were planted. So, 2/3 of the garden space was planted. There were a lot of words there, obfuscating the simplicity of the problem. Now, if only some of the divided gardens had been planted, that would have changed things.
*December 15, 2014*

**Algebra**

Hmmm. I see h(t), but no x. I expect you meant to ask what the t-intercept means. Reiny's answer would be the one you want. Generally in problems like this, x represents the distance traveled horizontally. So, in that case, the x-intercept wold be how far away the ball hit...
*December 15, 2014*

**7th grade math - tsk**

#1 is * not ^ Looks ok to me.
*December 15, 2014*

**maths**

69 is not a fraction. d = n+4 (n+1)/(d+1) = 4/5 (n+1)/(n+4+1) = 4/5 (n+1)/(n+5) = 4/5 5(n+1) = 4(n+5) 5n+5 = 4n+20 n = 15 The fraction was 15/19
*December 15, 2014*

**Pre-Algebra**

draw a diagram. Using similar triangles, h/60 = 5/10
*December 15, 2014*

**Calculus**

f(1) = 2-3+1 = 0 df = (6x^2-3) dx So, starting from f(1), f(0.8) = f(1)+(6-3)(-0.2) = -1.8 The line is y-0 = 3(x-1) You can see the approximation at http://www.wolframalpha.com/input/?i=plot+2x^3-3x%2B1%2C3%28x-1%29 You could have started with a different value of x, say, x=0....
*December 15, 2014*

**Calculus (math)**

You want to integrate along x, so the shells have thickness dx. The volume is thus v = ∫[1,6] 2πrh dx where r = x+2 and h = y = 1/x^4 v = 2π∫[1,6] (x+2)/x^4 dx That's a nice easy integral to evaluate.
*December 15, 2014*

**Calculus (math)**

s(t) = 1/4 t^3 - 5/3 t^3 + c The displacement is s(6)-s(-1) The distance traveled is the arc length. So, what steps did you follow?
*December 14, 2014*

**math**

use the good old quadratic formula: x = (-6±√(36+96))/(-16)
*December 14, 2014*

**Calculus (math)**

dQ/dt = kQ dQ/Q = k dt lnQ = kt + c Q = c*e^(kt) since 2 = e^(ln2), that can of course be written by massaging the constants as Q(t) = c*2^(-t/k) where k=35 Q(t) = c*2^(-t/35) Since we are given no actual amounts, we can set c=1, so that as a fraction of the initial amount, Q(...
*December 14, 2014*

**Calculus (math)**

you can find useful formulas here. Pick the one for a paraboloid and use your numbers. http://www.had2know.com/academics/paraboloid-surface-area-volume-calculator.html I'm sure you can derive it by calculating the arc length and revolving the curve. The Theorem of Pappus ...
*December 14, 2014*

**Calculus (math)**

probably true. I'll show you mine if you show me yours...
*December 14, 2014*

**Math**

5 rad = 5(180/pi deg) 5pi/8 rad = 5pi/8(180/pi deg) I expect you can do the simplification.
*December 14, 2014*

**Math**

draw your triangle. The standard ones with integer sides include 8-15-17
*December 14, 2014*

**Calculus**

f(-1) = -2 f(4) = -2 f(x) is differentiable in the interval, so the conditions are met, and the theorem applies. Extra credit: We want to show that for c somewhere in [-1,4] f'(c) = 0. f'(x) = 3-2x f'(x) = 0 when x = 3/2 3/2 is within the interval [-1,4], so the ...
*December 14, 2014*

**Calculus**

y' = 15x^4 - 75x^2 + 60 So, is y'(1) = 0?
*December 14, 2014*

**calculus**

It looks like this very problem is discussed at http://tutorial.math.lamar.edu/Classes/CalcIII/StokesTheorem.aspx f(x,y,z) is different, but the surface is a paraboloid just like yours. It goes through all the steps to evaluate the integral.
*December 14, 2014*

**Math**

If you meant 36 / (2^5/8) + 7 * (3+11) = 107 then yes. The spacing helped determine what you wanted, but parentheses work even better.
*December 14, 2014*

**Any Math Tutor Online? Help**

Geez. Draw some diagrams, ok? The distance x is (a) x =12cot3° - 12cot6° (b) x =12cot3° + 12cot6° (c) x^2 = (12cot3°)^2 + (12cot3°)^2
*December 14, 2014*

**Math**

No. It is 2^3 * 11 All you want is the prime factors, and their powers.
*December 14, 2014*

**Math**

teacher tells 6 students each of those tells 6 more, for 36 brand-new people. But the total is now the original 6 plus the 36 new ones. And so on for each generation. Yiu are correct in saying that next time, there were 6^3 = 216 new people told, but the original 6 and the ...
*December 14, 2014*

**Math**

6+36+216 Don't forget the people doing the telling!
*December 14, 2014*

**calculus**

y' = 4x+(9x^2/(3x^3+1)^(3/2)) y = 2x^2 - 2/√(3x^3+1) + C Now plug in (0,2) to find C. integrate using u = 3x^3+1, so du = 9x^2 dx
*December 14, 2014*

**Analytic Geometry**

7x+y-7=0 intersects x+y+1=0 at (4/3,-7/3). 7x+y-7=0 makes an angle of 98.13° x+y+1=0 makes an angle of 135° with the x-axis. So, the bisector makes an angle of 116.56°, with slope -2 So, the equation of the line is y + 7/3 = -2(x - 4/3) 3y+7 = -2(3x-4) 6x+3y+15=0 ...
*December 14, 2014*

**Physics**

solve for t in 50+19.6t-4.9t^2 = 0
*December 14, 2014*

**physic 210**

the distance traveled is 17t + 1/2 at^2 with t=5 and a=2. So, divide that by the circumference of the wheel = 2pi*48
*December 14, 2014*

**easy geometry**

For the trapezoid, all we really need is the altitude. You can surely then find the area and perimeter. The long base is 10 cm longer than the shorter one. So, draw altitudes at the end of the short base and you will see two right triangles with base 5 and hypotenuse 10. So, ...
*December 14, 2014*

**Math**

AD = AE-DE BE = AE-AB AB=DE, so AD = AE-AB = BE You can reword that using all the "congruents" instead of = signs.
*December 14, 2014*

**Physics**

initially, all the energy is KE = 1/2 mv^2 At the peak, all the KE has become PE = mgh So, with 2v at first, there's 4 times the KE. That means 4 times the height at the peak.
*December 13, 2014*

**Calculus 1**

As usual, draw a diagram. If the angle subtended by the arc walked around the lake is θ, then the distance traveled on foot = 4θ by boat = √(32(1+cosθ)) = 8cos(θ/2) Use the law of cosines to get this. So, the total time t is t = 4θ/10 + 8/5 cos...
*December 13, 2014*

**algebra 2**

x^2+2x-35 x = (-2±√(4+140))/2 = (-2±12)/2 = 5,-7 Not sure how you got your answers, since you declined to show your work... x^2+10x+24 (x+4)(x+6) or, using the QF, (-10±√4)/2 x^2-11x+24 (x-8)(x-3) or, via QF, (11±√25)/2
*December 13, 2014*

**Algebra**

If a4a5 means a4*a5, then clearly a4=1 and a5=13, making d=12. So, a3a6 = (-11)(25) = -275
*December 13, 2014*

**algebra 2**

if you are aiming for a perfect square, then you are correct.
*December 13, 2014*

**Math**

Sorry, make that the long multiplication button.
*December 13, 2014*

**Math**

(2x-1)(3x-7) = 6x^2-17x+7 go to calc101.com and click on the long division button. Enter 6x^2-17x+7 and 4x+3 as your polynomials, and watch the fun! I'm sure you will find where you went wrong.
*December 13, 2014*

**precalculus**

(A) The denominator never zero, so the domain is all real numbers. So, of course F(x) is continuous, since there are no places where it is undefined. As x gets large, F(x) ≈ 3x^2/x^2 = 3. For the zeros of rational functions, they occur where the numerator is zero (as ...
*December 13, 2014*

**Math**

If the ladder of length z touches the ground x feet from the fence, and touches the building at height y, then z^2 = (x+2)^2 + y^2 Using similar triangles we see that x/12 = (x+2)/y y = 12(x+2)/x z^2 = (x+2)^2 + (12(x+2)/x)^2 So, find dz/dx and set it zero, to see that the ...
*December 13, 2014*

**physics**

the answer, of course, is 10.0-6.14 = 3.86 kg have been removed.
*December 13, 2014*

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