已知sin(π/5-x)=3/5则cos(7/10π-x)=
问题描述:
已知sin(π/5-x)=3/5则cos(7/10π-x)=
答
sin(π/5-x)=3/5
cos【π/2-π/5+x】=3/5
cos(3π/10+x)=3/5
cos(7/10π-x)=cos【π-(3π/10+x)】= -cos(3π/10+x)= -3/5