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# 5 Mark Integration Question - Need Help. Tweet

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1. 5 Mark Integration Question - Need Help.

Mark Scheme

What I did..

I expressed cos2x in terms of cosx (because the question ask to but i can't relate to how it will help?)

(cos2x+1)/2 = cos^2 x

So i split the integral into --> (cos2x)(cos^2 x)^-1 --> (cos2x)(sec^2 x)

I integrated cos2x and got (1/2)sin2x and integrated sec^2 x which is tanx

I then multiplied both and got

(1/2)sin2xtanx

I then subd in my limits and my answer was nowhere near the answer in the MS. I have a feeling i did something wrong when i integrated?

Thanks.
2. Re: 5 Mark Integration Question - Need Help.
Can you use latex

I cannot see what you have done
3. Re: 5 Mark Integration Question - Need Help.

Mark Scheme

What I did..

I expressed cos2x in terms of cosx (because the question ask to but i can't relate to how it will help?)

(cos2x+1)/2 = cos^2 x

So i split the integral into --> (cos2x)(cos^2 x)^-1 --> (cos2x)(sec^2 x)

I integrated cos2x and got (1/2)sin2x and integrated sec^2 x which is tanx

I then multiplied both and got

(1/2)sin2xtanx

I then subd in my limits and my answer was nowhere near the answer in the MS. I have a feeling i did something wrong when i integrated?

Thanks.
Express the numerator as 2cos^2x - 1

therefore you get 2cos^2x - 1 / cos^2x = 2 - 1/cos^2x then integrate
Last edited by Extricated; 18-06-2012 at 21:33.