向量a=(ksinx,cosx),b=(cosx,-2cosx)函数f(x)=ab+1的图像经过点(pai/8,0)求函

f(x)
= a.b +1
=(ksinx,cosx).(cosx,-2cosx)+1
=ksinxcosx-2(cosx)^2+1
= (k/2)sin2x - cos2x
f(π/8)=0
(k/2) √2/2 -√2/2 =0
k=2
f(x)
= sin2x - cos2x
= √2(√(2/2)sin2x- (√2/2)cos2x)
=√2sin(2x-π/4)
最小正周期 = π