解得：x∈（π/4,π/2）,y∈（-3π/4,-π/2）∴x+y∈（-π/2,0）,x-y∈（3π/4,5π/4）又∵sin(x-y)=3/5,sin(x+y)=-3/5∴cos²（x-y）=1-9/25=16/25cos²（x+y）=1-9/25=16/25∴cos（x-y）=-4/5,cos（x+y）=...