A为钝角,但已知sinA=-5/13<0与这矛盾,题目错误!sinA=5/13A为钝角，sinA=5/13.得cosA=-[1-(sinA)^2]^(1/2)=-12/13,sin2A=2sinAcosA=2*5/13 *(-12/13)=-120/169 ;cos2A=1-2(sinA)^2=1-2*(5/13)^2=119/169 ;tan2A=sin2A/cos2A=-120/169/( 119/169)=-120/119。