If ∫ sec   2 x - 1 d x = α   log e cos   2 x + β + cos   2 x 1 + cos 1…

If sec 2x-1dx=α logecos 2x+β+cos 2x1+cos1βx   + constant, then β-α is equal to ______.

Solution

Given,

sec 2x-1dx=α logecos 2x+β+cos 2x1+cos1βx+C

Now solving L.H.S we get,

sec 2x-1dx=1-cos 2xcos 2xdx

sec 2x-1dx=2sin x2cos2x-1dx

Now let cos x=t -sin x dx=dt

sec 2x-1dx=-2dt2t2-1

sec 2x-1dx=-ln|2cos x+cos 2x|+C

=-12ln2 cos2x+cos 2x+2cos 2x·2 cos x+C

=-12lncos 2x+12+cos 2x·1+cos 2x+C

Now on comparing with sec 2x-1dx=α logecos 2x+β+cos 2x1+cos1βx+C

We get, β=12,α=-12β-α=1

Asked in: JEE Main 2023 (30 Jan Shift 2)

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