tan（a+π/4）=2tan(a+π/4-π/4)= [tan（a+π/4）-tan(π/4)]/[1+tan（a+π/4）tan(π/4)]=(2-1)/3=1/3所以sina/cosa=1/3cosa=3sinacos²a+sin²a=110sin²a=1 sin²a=1/10,cos²a=9/10sina co...