Question

△ABC,求证c&sup2分之a&sup2-b&sup2=sinC分之sin（A-B）【求大家帮忙解题~

Answer 1

证明：sin(A-B)/sinC=(sinA/sinC)*cosB-(sinB/sinC)*cosA

=a/c*（(a^2+c^2-b^2)/2ac）-b/c*((b^2+c^2-a^2)/2bc)

=(a^2-b^2)/c^2