已知函数f(x)=cos^2+sinxcosx(x属于R)

f(x)=cos^2+sinxcosx=(1+cos2x)/2+(sin2x)/2=(1/2)+[sin(2x+π/4)]/√2
f(3π/8)=(1/2)+(sinπ)/√2=1/2
f(x)的单调递增区间2x+π/4∈[(2k-1/2)π,(2k+1/2)π]
x∈[(k-1/8)π,(k+3/8)π]