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

$ \Rightarrow \,\,{\sin ^6}\theta  + {\cos ^6}\theta  + 3\,{\sin ^2}\theta \,{\cos ^2}\theta  = 1$

तथा ${\sin ^4}\theta  + {\cos ^4}\theta  + 2\,{\sin ^2}\theta \,{\cos ^2}\theta  = 1$

$\therefore$ $2\,\,({\sin ^6}\theta  + {\cos ^6}\theta ) – 3\,({\sin ^4}\theta  + {\cos ^4}\theta ) + 1 = 0$.