sin8分之7πcos8分之7π等于多少详细 过程,谢谢

sin8分之7πcos8分之7π等于多少
详细 过程,谢谢

sin(7π/8)cos(7π/8)
=(1/2)2sin(7π/8)cos(7π/8)
=(1/2)sin(7π/4)
=(1/2)sin(2π-π/4)
=(1/2)sin(π/4)
=(1/2)(√2)/2
=(√2)/4