已知sin(π-α)-cos(π+α)=根号2分之4,求sin(π+α)+cos(3π-α)的值
问题描述：
已知sin(π-α)-cos(π+α)=根号2分之4,求sin(π+α)+cos(3π-α)的值
答
化简后发现右式与左式为相反数,即右式=-√2/4
sin(a+b)=sinacosb+cosasinb
sin(a-b)=sinacosb-cosasinb
cos(a+b)=cosacosb-sinasinb
cos(a-b)=cosacosb+sinasinb