If b n = ∫ 0 π 2 cos 2 n x sin x d x , n ∈ ℕ , then

If bn=0π2cos2nxsinxdx,n, then
  1. b3-b2,b4-b3,b5-b4 are in an A.P. with common difference-2
  2. 1b3-b2,1b4-b3,1b5-b4 are in an A.P. with common difference 2
  3. b3-b2,b4-b3,b5-b4 are in a G.P.
  4. 1b3-b2,1b4-b3,1b5-b4 are in an A.P. with common difference -2

Solution

Given,

bn=0π21+cos2nxsinxdx

bn+1-bn=0π2cos2n+1x-cos2nxsinxdx

=0π2-sin2n+1xsinxsinxdx

=cos(2n+1)x2n+10π2=-12n+1

So,1b3-b2=-5

1b4-b3=-7

1b5-b4=-9

So,1b3-b2,1b4-b3,1b5-b4 are in A.P. with c.d=-2

Asked in: JEE Main 2022 (25 Jun Shift 2)

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