A5 The simplified expression $(\sin x+2 \cos x)^{2}+(2 \sin x-\cos x)^{2}$ is equal to:
(A) 0
(B) $3 \sin x+\cos x$
(C) $\cos 2 x$
(D) 1
(E) 5
A5. In the expression, we remove the parentheses and get $5 \sin ^{2} x+5 \cos ^{2} x=5\left(\sin ^{2} x+\cos ^{2} x\right)=5 \cdot 1=5$.