若是sinx+cosx
则 =√2(cos45°sinx+cosxsin45°)=√2sin(45+x)
-√2≤√2sin(45+x)≤√2
若是sinx-cosx
则 =√2(cos45°sinx-cosxsin45°)=√2sin(45-x)
-√2≤√2sin(45-x)≤√2
若是sinxcosx
则sinxcosx=1/2sin2x
-1≤sin2x≤1
-1/2≤sinxcosx≤1/2
若是sinx+cosx
则 =√2(cos45°sinx+cosxsin45°)=√2sin(45+x)
-√2≤√2sin(45+x)≤√2
若是sinx-cosx
则 =√2(cos45°sinx-cosxsin45°)=√2sin(45-x)
-√2≤√2sin(45-x)≤√2
若是sinxcosx
则sinxcosx=1/2sin2x
-1≤sin2x≤1
-1/2≤sinxcosx≤1/2