m=-2sinx-cosx

m=√[(-2)？ +(- 1)? ]sin(x+α)(0 & lt； α& lt； π/2)

m=√5sin(x+α)

So the value range of m is [-√5, √5].

Note: This is a commonly used trigonometric function deformation formula, which uses the sin(α+β) formula. In fact, sinα =-1√ 5.

Or cosα=-2/√5.