sin(α+β)=cosαsinαcosβ+cosαsinβ=cosα-4sinα/5+3cosα/5=cosα-4sinα/5=2cosα/5tanα=-1/2tanβ=-3/4tan(α+β) =(tanα+tanβ)/(1-tanαtanβ)=(-5/4)/(1-3/8)=(-5/4)/(5/8)=-2