已知cos(a+π/4)=3/5,π/2≤a≤3π/2,求cos(2a+3π/4)的值

问题描述:

已知cos(a+π/4)=3/5,π/2≤a≤3π/2,求cos(2a+3π/4)的值

因为cos(a+π/4)=3/5>0,
π/2