>>596
Cos[x]Sin[x]+Cos[2x] = 1/2*Sin[2x]+Cos[2x] = √5/2(1/√5*Sin[2x] + 2/√5*Cos[2x])
= √5/2*Sin[2x + α] (tanα=2)
-√5/2≦√5/2*Sin[2x + α]≦√5/2