设x=sina(a∈[-π/2,π/2]),方程变为cosa=sina+m,
所以m=cosa-sina=-√2sin(a-π/4)
∵a∈[-π/2,π/2],∴a-π/4∈[-3π/4,π/4],
∴sin(a-π/4)∈[-1,√2/2],∴y∈[-√2,1]
因为方程无解,所以m1