a=b+c-2bc cosA a=3+5-2*3*5*cos120° a=49 a=7 ∵a/sinA=b/sinB ∴7/sin120°=3/sinB ∴sinB≈0.371 ∵a/sinA=c/sinC ∴7/sin120°=5/sinC ∴sinC≈0.619