(1)sin(a+b)=1/2,sin(a-b)=1/3,则sinacosb+cosasinb=1/2,sinacosb-cosasinb=1/3,则sinacosb=5/12,cosasinb=1/12,所以sinacosb=5cosasinb(你抄错题了吧）（2）由（1）中将cosb除到右边将cosa除到左边即可得
