Question

已知cosA+sinA=-[7/13]，A为第二象限角，则tanA=（　　）

Answer 1

cosA+sinA=-7/13[(cos^2)0.5A+(sin^2)0.5A]

(cos^2)0.5A-(sin^2)0.5A+2sin0.5Acos0.5A=-7/13[(cos^2)0.5A+(sin^2)0.5A]

同除(cos^2)0.5A，设t=tan0.5A

1-t^+2t=-7/13(1+t^2)

求出t即tan0.5A，结合象限，再求出tanA