sinα·cosα=1/8,0°

问题描述:

sinα·cosα=1/8,0°

0°(cosα+sinα)²=1+2sinα·cosα=5/4
cosα+sinα=根号5/2

用a代替
0则cosa>sina
cosa-sina>0
(cosa+sina)²
=cos²a+sin²a+2sinacosa
=1+2*1/8
=5/4
所以cosa-sina=√5/2