sin8x cos12x+ sin12x cos8x=sin(8x+12x)=sin20x
sin20x≥1/2, π/6+2πn≤20x≤5π/6+2πn,
π/120+πn/10≤x≤5π/120+πn/10, n∈Z
sin8x cos12x+ sin12x cos8x=sin(8x+12x)=sin20x
sin20x≥1/2, π/6+2πn≤20x≤5π/6+2πn,
π/120+πn/10≤x≤5π/120+πn/10, n∈Z