(3)[解法一]令 f(x)=sinx+cosx，α=
则g(x)=f(x+α)= sin(x+
=cosx-sinx，
于是h(x)= f(x)·f(x+α)
= (sinx+cosx)(cosx-sinx)
=cos2x.
[解法二]令f(x)=1+
g(x)=f(x+α)= 1+
=1-
= (1+
)
sinx)