已知在 △ABC\bigtriangleup {ABC}△ABC 中, A+B=3C,2sin(A−C)=sinBA + B = {3C},2\sin \left( {A - C}\right) = \sin BA+B=3C,2sin(A−C)=sinB .(1) 求 sinA\sin AsinA ；(2)设 AB=5{AB} = 5AB=5 ，求 AB{AB}AB 边上的高.