求[cos(3/4pai)]^4-[sin(3/4pai)]^4的值

cos(3/4pai)=cos(π-π/4)=cosπcosπ/4+sinπsinπ/4=-√2/2sin(3/4pai)=sin(π-π/4)=sinπcosπ/4-cosπsinπ/4=sinπ/4=√2/2[cos(3/4pai)]^4-[sin(3/4pai)]^4=(-cosπ/4)^4-(sinπ/4)^4=(-√2/2)^4-(√2/2)^4=(...