向量a⊥向量b
cosφ = sinφ
φ = pi/4
周期为pi
w = 2
f(x) = sin(2x+pi/4)
g(x) = sin(2(x-6)+pi/4）= sin (2x - 12 + pi/4)
-pi/2 < 2x - 12 + pi/4 < pi/2
6 - 3pi/8 < x < 6 + pi/8单调递增区间