cosA=-5/13 可得：sinA=12/13cosB=3/5 可得：sinB=4/5sinC=sin(A+B) =sinAcosB+cosAsinB =12/13 x 3/5 + (-5/13) x 4/5 =16/652、根据正弦定理可得：BC/sinA=AC/sinB所以可得：AC=BCsinB/sinA =(5 x 4/5)/ (12/13) =13/3S△=ACxBC x sinC/2 =13/3 x 5 x 8/65 =8/3