1,f(x)=a·b=4sinx*2cosx-4√6(cosx+sinx)*cos(x+π/4)
=4sin(2x)-4√6(cosx+sinx)*(√2/2cosx-√2/2sinx)
=4sin(2x)-4√3[(cosx)^2-(sinx)^2]
=8[1/2sin(2x)-√3/2cos(2x)]
=8[sin(2x)cosπ/3-cos(2x)sinπ/3]
=8sin(2x-π/3).
当x∈[π/4,π/2]时,π/6