Răspuns :
E = √5 sin 2x -cos 2x, daca tg x =√5/2
√5 sin 2x - cos 2x⇒ √5 sin 2x = cos 2x⇒ (√5 sin 2x)/(cos 2x)=1⇒
E(x) = √5×tg 2x
dar tg 2x = 2tg x /(1-tg²x)
deci E (x) = √5×[2 tg x/(1-tg²x)
[2×(√5/2)] /(1-[(√5)²/4]=√5/[1-(5/4)]=-4√5
E(x) = √5 × (-4√5)=-4×5 =-20