sinx+cosx=√2(√2/2*sinx+√2/2*cosx)
=√2(cos45°*sinx+sin45°*cosx)
=√2sin(x+45°)
所以 -√2≤√2sin(x+45°)≤√2
故-√2≤sinx+cosx≤√2
即-√2≤√2m≤√2
-1≤m≤1
sinx+cosx=√2(√2/2*sinx+√2/2*cosx)
=√2(cos45°*sinx+sin45°*cosx)
=√2sin(x+45°)
所以 -√2≤√2sin(x+45°)≤√2
故-√2≤sinx+cosx≤√2
即-√2≤√2m≤√2
-1≤m≤1