MCQ
${\sin ^6}\theta + {\cos ^6}\theta + 3{\sin ^2}\theta {\cos ^2}\theta = $
  • A
    $0$
  • B
    $-1$
  • $1$
  • D
    None of these

Answer

Correct option: C.
$1$
c
(c) ${\sin ^6}\theta + {\cos ^6}\theta + 3\,{\sin ^2}\theta \,{\cos ^2}\theta $

$ = {({\sin ^2}\theta + {\cos ^2}\theta )^3} - 3{\sin ^2}\theta {\cos ^2}\theta + 3{\sin ^2}\theta {\cos ^2}\theta = 1.$ 

Trick : Put $\theta = {0^o},$

we get the value of expression equal to $1. $

Again put $\theta = {45^o},$ the value remains $1,$ it means that the expression is independent of $\theta$ and is equal to $1.$

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