已知a∈(π/4,3π/4),b∈(0,π/4),cos(π/4-a)=4/5,sin(3π/4,b)=5/13,求cosa,sin(a+b)的值
问题描述:
已知a∈(π/4,3π/4),b∈(0,π/4),cos(π/4-a)=4/5,sin(3π/4,b)=5/13,求cosa,sin(a+b)的值
答
为a∈(π/4,3π/4),b∈(0,π/4),所以π/4