25X^2-5X-12=0 (5X+3)(5X-4)=0 X1=4/5,X2=-3/5 因为a属于（0,π）,sina>=0
所以,sina=4/5,coa=-3/5
(1)
sin^2a-cos^2a=7/25
(2)tana+cota=sina/cosa+cosa/sina=(sin^2a+cos^2a)/(sinacosa)=1/(-12/25)=-25/12