已知sin a=根号5/5,则sin4 a-cos4 a的值为多少
问题描述:
已知sin a=根号5/5,则sin4 a-cos4 a的值为多少
答
sin^4α-cos^4α =(sinα+cosα)(sinα-cosα) =-cos(2α) =2sinα-1 =2*(-√5/5)-1 =2*(1/5)-1 =-3/5
已知sin a=根号5/5,则sin4 a-cos4 a的值为多少
sin^4α-cos^4α =(sinα+cosα)(sinα-cosα) =-cos(2α) =2sinα-1 =2*(-√5/5)-1 =2*(1/5)-1 =-3/5