∫π/3π/6dxsecx+cscx=√a−b2+√c2log(√d+√e−√f−g)
I had to solve the integral and get it in this form. However, I cannot understand what to do.
My attempt:
∫π/3π/6dxsecx+cscx
=∫π3π6sinxcosxsinx+cosxdx
Substituting t=tan(x2),
∫tan(π6)tan(π12)2t1+t2×1−t21+t2×21+t2dt
2∫1√32−√32t(1−t2)(1+t2)3dt
Substituting u=1+t2, 2tdt=du, 1−t2=2−u
2∫438−4√3(2−u)u3du
4∫438−4√3duu3−2∫438−4√3duu2
After integrating this last step, I had thought I would substitute back u=1+t2=1+tan2(x2). However, this doesn't seem to give me the required value. Could somebody please tell me where I have gone wrong? Also could someone please tell me how to change the limits of the definite integral throughout? This is the first time I have used a Weierstrass Substitution and so I don't know how to change the limits.
Please do help me!
Really, really grateful for your help!
Answer
Here is an alternate method you could use:
Multiply ∫sinxcosxsinx+cosxdx on the top and bottom by cosx−sinx to get
∫cos2xsinx2cos2x−1dx−∫sin2xcosx1−2sin2xdx.
Now substitute u=cosx in the first integral and u=sinx in the second integral to get
∫u21−2u2du=12∫(−1+11−2u2)du=12[−u+√24ln|1+√2u1−√2u|]+C
using partial fractions.
Now you can let u=cosx in the first term and u=sinx in the second to get
12[−u+√24ln|1+√2u1−√2u|]12√32−12[−u+√24ln|1+√2u1−√2u|]√3212
Notice that substituting t=tanx2 gives
∫sinxcosxsinx+cosxdx=∫2t1+t2⋅1−t21+t22t1+t2+1−t21+t2⋅21+t2dt=∫4t(1−t2)(1+t2)2(1+2t−t2)dt,
and now you can use partial fractions to continue.
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