Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: I need this now very

  1. Jun 22, 2005 #1
    plz i need this now very urgent

    integral (2- (sinx)^2) * (2+ (sinx)^2) / (cos x)^2 plz now
     
  2. jcsd
  3. Jun 22, 2005 #2
    Hi Sabine what can you do with your double angle formulae here?

    [tex] 1- cos2x = 2sin^2x [/tex]
    [tex] 1/2(cos2x +1) = cos^2x [/tex]
     
    Last edited: Jun 22, 2005
  4. Jun 22, 2005 #3
    it can be int(4- sin^2 x)/ cos^2 x dx = int(3+ cos^4 x)\ cos^2 x dx= 3(1+tan^2 x) + 1\tanx
     
  5. Jun 22, 2005 #4
    hi monet 2sin^2 x = 1- cos 2x this means what u wrote is wrong .
     
  6. Jun 22, 2005 #5

    oops yeah sorry nowhere near a mentor here I just did a quick rearrange of the equation I was looking at to post it probably should have left that part alone, all I really have to offer is that the double angle formulas can really crack open the integral for you, have you applied them?

    edit: I am not being real clear am I :redface: what I mean is tht I looked at the integral for you because you said its urgent (I'd normally butt out and leave it to the graduates) and I see that if you multiply out the numerator you'll get a simpler integral to manipulate with the double angle formula.
     
    Last edited: Jun 22, 2005
  7. Jun 22, 2005 #6
    well i tried i jst managed to find the solution i wrote before
     
  8. Jun 22, 2005 #7
    (2- (sinx)^2) * (2+ (sinx)^2) / (cos x)^2
    = (4 - (sinx)^4)/(cos x)^2
    = (4 - {(sinx)^2}^2)/(cos x)^2
    = (4 - {1 - (cosx)^2}^2)/(cos x)^2
    = (4 - {1 - 2(cosx)^2 + (cosx)^4})/(cos x)^2
    = (3 + 2(cosx)^2 - (cosx)^4)/(cos x)^2
    = (3/(cos x)^2) + 2 - (cos x)^2
    = (3/(cos x)^2) - (1/2)*{2(cos x)^2 - 1 - 3}
    = (3/(cos x)^2) - (1/2)*{cos(2x) - 3}
    = 3(sec x)^2 - (1/2)cos(2x) + (3/2)

    integral = 3*tan(x) - (1/4)*sin(2x) + (3/2)*x + C
     
    Last edited: Jun 22, 2005
  9. Jun 22, 2005 #8
    brilliant geosonel
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook