Sunday

May 29, 2016
Total # Posts: 26,282

**Science**

model ? example Bohr atom ?
*January 3, 2016*

**Calculus**

http://mathworld.wolfram.com/Semicircle.html look at integration for weighted mean, then divide by area. pi r^2/2
*January 3, 2016*

**Calculus**

4 r/3pi is the semicircle do the outer one, then subtract the inner one. See for example: http://en.wikipedia.org/wiki/List_of_centroids
*January 3, 2016*

**math**

(-1)^ even power = 1
*January 3, 2016*

**Math**

it is 4, the distance from west 2 to east 2 :)
*January 3, 2016*

**Math**

n^2 - 4 = 21 + 9 n n^2 - 9 n -21 = 0 (n-7)(n+3) = 0 n = 7 so the smallest is 5
*January 3, 2016*

**Math**

They are POSITIVE, odd numbers are OUT so they differ by TWO n-2 , n , n+2 (n-2)(n+2) = 21 + 9 n
*January 3, 2016*

**math**

x^4 - 5 x^3 + 5 x^2 + 4 x - 61 = 0 find the roots try http://www.wolframalpha.com/input/?i=x^4+-+5+x^3+%2B+5+x^2+%2B+4+x+-+61+%3D+0+&x=5&y=5
*January 3, 2016*

**Algebra**

55 t +120 - 40 t = 135 15 t = 15 t = 1 hour at 55 so 55 miles on highway 2 hours at 40 = 80 miles on dirt
*January 3, 2016*

**Algebra**

55 t + 40 (3-t) = 135
*January 3, 2016*

**math**

I will leave you to get s now
*January 3, 2016*

**math**

.866 s = 950 sin h - 90 .866 s = 1645 cos h ---------------------subtract 950 sin h = 1645 cos h + 90 or 950 sin h - 1645 cos h = 90 for various values of h h , left side 60 , .224 61 , 33.4 62 , 66.5 63 , 99.6 so steer 62.5 degrees west of south 65 , 165 70 , 331
*January 3, 2016*

**math**

He must stay on a course of S 60 W. We must find the heading :) h is degrees heading west of south say his speed over the ground is s then west speed over ground = s sin 60 = 950 sin h - 90 and south speed over ground = s cos 60 = 950 cos h so .866 s = 950 sin h - 90 .5 s = ...
*January 3, 2016*

**Does not make sense**

You say Ruth has 130 then ask how much she has.
*January 3, 2016*

**Geography (Ms.Sue ) Help**

Interesting - stress seems to lead to more babies. War torn Afganistan is top at 2.4 followed by Maldives threatened by flooding at 1.9 Quiet but lonely Nepal at 1.2 Quiet Sri Lanka (since the tsunami) lowest at 0.8
*January 3, 2016*

**Geography (Ms.Sue ) Help**

http://www.google.com/search?q=population+growth+nepal&ie=utf-8&oe=utf-8 http://www.google.com/search?q=population+growth+afganistan&ie=utf-8&oe=utf-8 http://www.google.com/search?q=population+growth+sri+lanka&ie=utf-8&oe=utf-8 http://www.google.com/search?q=population+growth+...
*January 3, 2016*

**math**

6-4 5-3 4-2 3-1 4-6 3-5 2-4 1-3 so 8 work out of how many 6 * 6 I think or 36 so I get 8/36 = 2/9 see: http://www.freemathhelp.com/rolling-dice.html
*January 3, 2016*

**physics**

Ah, did not think of that :)
*January 3, 2016*

**physics - No way - directions not defined**

Is it pushed up or down the slope? Is that 20 m/s up slope or down slope? I will assume both are UP and you will have to get it straight yourself. weight component down slope = m g sin 37 = 80 * 9.81 * sin 37 = 472 N If you are pushing up with 400 N, you lose, at least on ...
*January 3, 2016*

**chemistry**

Maybe lea nitrate ?
*January 3, 2016*

**math**

a7 = a + d(6) = 21 {so 2a+12 d = 42} sum of first 13 = (13/2)(2a + 12d) = (13/2)(42) = 13 * 21 = 273 look at: http://www.mathsisfun.com/algebra/sequences-sums-arithmetic.html
*January 3, 2016*

**Calculus pz help urgently**

-.25 cos (2x-pi/4) - .25 x sqrt 2 + c
*January 3, 2016*

**Calculus pz help urgently**

note we no longer have sine curves with zero mean value but now have an average plus a cosine curve with twice the frequency.
*January 3, 2016*

**Calculus pz help urgently**

note sin pi/4 = sqrt2/2 -.25 cos (2x-pi/4) - .25 sqrt 2
*January 3, 2016*

**no, wrong**

I guess maybe you mean sin x cos(x-pi/4)dx sin x cos y = .5 sin (x+y) + .5 sin (x-y) (remember "beat frequency" ) so .5sin ( 2x-pi/4)dx + .5sin (pi/4)dx
*January 3, 2016*

**Calculus pz help urgently**

I guess maybe you mean sin x cos(x-pi/4)dx sin x cos y = .5( sin x +sin y) + .5 (sin x - sin y) (remember "beat frequency" ) so .5(sin x + sin(x-pi/4)dx + .5(sin x - sin(x-pi/4)dx ---------------------------- add (oh my) sin x dx -cos x + c
*January 3, 2016*

**sorry, do not know**

As far as I know zero to the anything is zero.
*January 3, 2016*

**Math**

You are welcome.
*January 3, 2016*

**Math**

a) 2/7 b) 5/7 * 9/24 c) assume 6 am for maximum inconvenience so 8/24
*January 3, 2016*

**math**

20/16 divide top and bottom by 4 5/4
*January 3, 2016*

**math**

still 5/4
*January 3, 2016*

**Math**

c T = wavelength - 3 m (1/4)3 = .75 meters = 750 cm
*January 3, 2016*

**Math**

how long would a (1/4) wave antenna be? (use c = 3*10^8 meters/second)
*January 3, 2016*

**math- HELP!**

$2600 initial at 8% compounded continuously
*January 2, 2016*

**Do you get it now?**

Get the idea? Richer # = log of amplitude. so you take 27 times the antilog and then take the log of that
*January 2, 2016*

**Math Exponetial Function Problem Question?**

here slowly Richer number = 3.2 3.2 is log of amplitude A log A = 3.2 10^logA = A = 10^3.2 = 10^3 * 10^.2 so A = 10^3 * 1.5848 Now Multiply THAT by your 27 B = 10^4 * 4.27921 log B = log 4 + log 4.27921 = 4.631 which is your new Richter #
*January 2, 2016*

**Math Exponetial Function Problem Question?**

You multiply the 27 by the amplitude, not the log of the amplitude. then take the log of the new bigger amplitude for the new Richter number.
*January 2, 2016*

**Math Exponetial Function Problem Question?**

No, log scale I answered this yesterday http://www.jiskha.com/display.cgi?id=1451681946
*January 2, 2016*

**Spanish**

whew :)
*January 2, 2016*

**Math**

I did this not long ago http://www.jiskha.com/display.cgi?id=1451681946
*January 2, 2016*

**Math**

hint here: http://www.jiskha.com/display.cgi?id=1451675195
*January 2, 2016*

**Math**

You are welcome.
*January 2, 2016*

**Math**

Suspect you mean 2^(2x+3) = 80 that means (2x+3)log 2 = log 80 (2x+3) = 6.32192 2x = 3.32192 x = 1.6609
*January 2, 2016*

**Math**

19 * 100 / 27 = 70 % is his score in percent. I do not know if you are using letter grades or whatever.
*January 2, 2016*

**Math**

I think your answer is fine. So is the 3^2 = 9 one.
*January 2, 2016*

**Math**

well 9^x = 3^(2x) so log^-1 (2 x log 3) is a perfectly good answer. So is Log^-1(xlog(9)) They are the same :)
*January 2, 2016*

**Math**

Yes, but count brackets. I try to use different ones log^-1[ x(log 7 - log 8) ]
*January 2, 2016*

**Calculus**

It is just that sqrt (a^2-b^2) is not a - b
*January 2, 2016*

**Calculus**

By the way, you tried x^3 as well :..... sqrt (1-x^6) into 1^(1/2)- x^(3) ..."
*January 2, 2016*

**Calculus**

Why should I not let u = anything I choose ? LOL I see an x^6 and an x^2 so I tried x^3
*January 2, 2016*

**Calculus**

sin^-1 u + c so sin^-1 x^3 + c
*January 2, 2016*

**Calculus**

sqrt (1-x^6) into 1^(1/2)- x^(3) I do not think so I will try the easy way u = x^3 du = 3 x^2 dx so I have du/ sqrt (1-u^2)
*January 2, 2016*

**Calculus**

B and D
*January 2, 2016*

**Calculus**

In C, that nasty x cancels
*January 2, 2016*

**Calculus**

the problem with B and D is that dx = dy/f(x) so the substitution does not get rid of the x
*January 2, 2016*

**Calculus**

I had trouble with B and D
*January 2, 2016*

**Calculus**

∫√(x^2-1) dx <---- NOTE that dx let y = x^2-1 then dy = 2 x dx so dx = dy/2x ∫√(x^2-1) DX =∫y^.5 dy/2x a mess again
*January 2, 2016*

**Calculus**

You are wrong. A CAN easily be solved Be sure to include the dx in your integrals so you include it when you substitute
*January 2, 2016*

**Calculus**

B. let y = 1 - x^2 dy = -2 x dx ∫1/√(1-x^2) dx = ∫y^-.5 dy/(-2x) very awkward Hey be sure to include the dx in your integrals C will be easy because the x in -2xdx cancels
*January 2, 2016*

**Calculus**

A. let y = x-1 dy = dx ∫√(x-1) = ∫y^.5 dy that works
*January 2, 2016*

**Calculus**

You are welcome.
*January 2, 2016*

**Calculus**

∫(x^3-x^2) dx/x^2 =∫(x^3/x^2-x^2/x^2)dx = ∫(x^3/x^2-x^2/x^2)dx = ∫(x-1)dx = (x^2/2) - x + c which is the fourth option and is also what you got
*January 2, 2016*

**spanish**

If you are not sure and you are taking Spanish, we have a serious problem here :)
*January 2, 2016*

**spanish**

Lives in a hotel and is rich and spends much money Does not respect Mexicans or appreciate their clothes. But, interestingly Peace Corps volunteers must come from a different country entirely :)
*January 2, 2016*

**World Civilizations**

Of course there was introducing the natives to Christianity. I do not think I will follow that train of thought further and have deleted a sentence or two.
*January 2, 2016*

**Physics of ice skating**

Well, I guess the skate you are pushing with is at an angle so the long sharp edge can get a grip on the ice while the forward skate moves forward straight ahead. I had never thought about it but that is the way you skate although 45 degrees seems kind of extreme. If you look ...
*January 2, 2016*

**Hmm, I can not help**

... but if you do get help, let me know. We have three dogs that desperately need training. Luckily they are tiny.
*January 2, 2016*

**clickable link I hope**

http://en.wikipedia.org/wiki/Pacific_Route
*January 2, 2016*

**Social Studies (Check, Please!)**

I might go a bit further and claim that Russia would have collapsed without the convoys to Murmansk and to their Pacific seaport Vladivostok. https://en.wikipedia.org/wiki/Pacific_Route
*January 2, 2016*

**Math**

c * 11.5 + p * 13 = 1255 c + p = 100
*January 2, 2016*

**math**

You are welcome.
*January 2, 2016*

**math**

For example: Boole was appointed to the chair of mathematics at Queens College, Cork in 1849. In fact he made an application for a chair in any of the new Queen's Colleges of Ireland in 1846 and in September of that year De Morgan, Kelland, Cayley, and Thomson were among ...
*January 2, 2016*

**math**

http://www-history.mcs.st-andrews.ac.uk/Biographies/Boole.html
*January 2, 2016*

**Math**

No problem. You are welcome.
*January 2, 2016*

**Math**

Angle at C is common to triangles ACD and to ACB since angles in both triangles add to 180, angle ADC = twice angle ABD call angle CAD = T then BAD = T call angle ABD = A then angle ADC = 2A then sin T / 6 = sin 2A /x sin 2T / 11 = sin A /x sin T / 5 = sin (180-2A)/8 = sin 2A...
*January 2, 2016*

**Physics**

I did this a few days ago. http://www.jiskha.com/display.cgi?id=1451329598
*January 2, 2016*

**maths**

3/4*1/3 = 1/4
*January 2, 2016*

**Calculus help plz**

Thanks for figuring out what was meant. I just threw up my hands in frustration.
*January 2, 2016*

**Calculus**

Happy to help :)
*January 2, 2016*

**Calculus Huh??**

Is this supposed to be: ∫((cos^3(x)/(1-sin^2(x)) dx ?? 1 - sin^2 x = cos^2 x because cos^2 x + sin^2 x = 1 so you have ∫ cos(x) dx the derivative of the integral is what you already have, cos x the integral is sin x + c
*January 2, 2016*

**Physics**

m g = 2890 m g - 2200 = m (.36) You did not say what your question is but you can solve that for m and for the local g
*January 2, 2016*

**Math**

depends what you mean by intense. If amplitude is 27 times log A = 3.2 so A =1584 B = 1584 * 27 = 42792 log B = 4.63
*January 1, 2016*

**mechanics**

You are asking me to write a chapter in your text book. Any physics text can help you better than I can. for the first question: F = G Me m/r^2 = (GMe/r^2) m for changes in r that are small compared to earth radius, like from here to the top of Mt Everest this quantity is ...
*January 1, 2016*

**physics**

40 cycles / (8*60 seconds) = .083 Hz
*January 1, 2016*

**Physics**

How long to fall 46-1.8 = 44.2 meters ? 44.2 = (1/2) g t^2 t = sqrt (88.4/9.81) t = 3 seconds d = u t = 1.20 * 3 = 3.6 meters
*January 1, 2016*

**Reposting calculus help plz**

y dy = x dx + x^3 dx y^2/2 = x^2/2 + x^4/4 + c
*January 1, 2016*

**mechanics**

torque = moment of inertia * angular acceleration 40 * 0.20 = 30 alpha alpha = .267 radians/sec^2 omega = alpha * t omega= .267 * 4 = 1.07 radians/sec angle = (1/2) alpha *t^2 = .5 *.267 *16 = 2.136 radians divide by 2 pi = .34 revolutions torque * angle = work in = 8 * 8.53...
*January 1, 2016*

**Maths**

assume you mean 24 m not cm distance d from tree tan 45 = (24-h)/d tan 60 = h/d so (24-h)/tan 45 = h/tan 60
*January 1, 2016*

**Maths/physics need help agn**

up force from each student = 81 N = F cos 60 = F/2 so 162 N
*January 1, 2016*

**Maths/physics**

(1/2) m v^2 = (1/2) k x^2 .5 (1600) = .5 k (.04) k = 40,000 Newtons/meter F = k x = 40,000 (.2) = 8000 N
*January 1, 2016*

**maths**

area of brick = .25*.12 = .03 m^2 area of yard = 20*30 = 600 m^2 number of bricks = 600/.03 = 20,000
*January 1, 2016*

**Math parentheses ?**

do you mean 3 - x = sqrt (x^2 - 5) ?? if so 9 - 6 x + x^2 = x^2 - 5 6 x = 14 x = 7/3 = 2.33 x^2 - 5 must be + so |x| >/= sqrt 5 or 2.24
*January 1, 2016*

**Calculus**

hanging mass = 100 + 2 x F = g(100+2x) do dW = F dx from x = 0 to x = 20 W = g (100 x + x^2) at 20 - at 0 = g (2000 + 400) = g (2400) = 23520 Joules then from x = 0 to x = 10 g (1000 + 100) = 1100 g = 10780 Joules subtract I get 12740 Joules
*December 31, 2015*

**Electric field**

(1/2) m v^2 = q V m is electron mass q is electron charge (assume positive)
*December 31, 2015*

**Trig**

CSC (5PI/6) ?? 6pi/6 or pi is 180 degrees, the - x axis so we are pi/6 or 30 degrees above the - y axis the sin of that angle (150 deg) is 1/2 so the answer is 1/(1/2) or 2
*December 31, 2015*

**physics**

Torque = I alpha 5.2 * .8 = 1.4 alpha alpha = 2.97 radians/second^2
*December 31, 2015*

**physics**

The current now has three choices for where to go, but the voltage is the same for all three. itotal = V/R + V/r + V/R itotal = 3 V/R = V/(R/3) which is the voltage divided by the equivalent resistance, R/3
*December 31, 2015*

**Science**

The type of force is therefore electrostatic (Coulomb) force in the simple model of atoms.
*December 31, 2015*

**Science**

I am no chemist but those are all compounds between Hydrogen and halogens which desperately want to grab an electron to fill their outer shells so I would expect Hydrogen bonds where the Hydrogen partially gives up its sole electron.
*December 31, 2015*

**Electric field**

1 electron volt or 1.6*10^-19 Joule
*December 31, 2015*