f(sinx+cosx)=(sinx+1)(cosx+1),
sinx+cosx=1/2,
(sinx+cosx)^2=1/4,
sinxcosx=-3/8,
f(1/2)=(sinx+1)(cosx+1)=sinxcosx+sinx+cosx+1=-3/8+1/2+1=9/8.