Un = cos^n thita + sin^n thita.
2U6 - 3U4 is equal to??
(a) 0 (b) 1 (c) -1 (d) none of these

(U4-U2)^2 is equal to ???
(a)1/4sin^4 2thita (b)sin^4 2thita (c)4sin^4 2thita (d) none of these

Dear student
Given: Un=sinnθ+cosnθThen 2U6-3U4=2sin6θ+cos6θ-3sin4θ+cos4θ=sin4θ2sin2θ-3+cos4θ2cos2θ-3=sin4θ2sin2θ-2-1+cos4θ2cos2θ-2-1=sin4θ-21-sin2θ-1+cos4θ-21-cos2θ-1=sin4θ-2cos2θ-1+cos4θ-2sin2θ-1=-2sin4θcos2θ+sin4θ+2cos4θsin2θ-cos4θ=-sin4θ+cos4θ+2sin2θ cos2θsin2θ+cos4θ=-sin2θ2+cos2θ2+2sin2θ cos2θ=-sin2θ+cos2θ=-1
Regards

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