sin^2a+cos^2a=1;sin^2(a-b/2)=144/169,0＜a-b/2＜180o；sin(a-b/2)=12/13;cos^2(a/2-b)=9/25; 0 ＜ a/2-b＜90o;cos(a/2-b)=3/5;又（a+b)/2=(a-b/2)+(a/2-b);sin(a+b)=2sin((a+b)/2)cos((a+b)/2)=2sin[(a-b/2)+(a/2-...