a=(√3,cosx),b=((cosx)^2,sinx))
f(x) = a.b - √3/2
=(√3,cosx).((cosx)^2,sinx) -√3/2
=√3(cosx)^2+sinxcosx -√3/2
=(√3/2)(1+cos2x) +(1/2)sin2x - √3/2
= sin(2x+ π/3)
增區(qū)間
2nπ- π/2≤2x+ π/3≤2nπ+ π/2
nπ -π/12 ≤ x ≤ nπ + π/12
if x∈[0,π/4]
1/2≤f(x) ≤1
x = x'-π/6
f(x')成為奇函數(shù)