根据sina*sinb=[cos(a-b)-cos(a+b)]/2sinx·sin(x-π/4)=[cosπ/4-cos(2x-π/4)]/2=[√2/2-cos(2x-π/4)]/2显然上式在cos(2x-π/4)=1时取最小值为(√2/2-1)/2=√2/4-1/2
