Question

已知sinx=1/4,cosB=-1/3,x,B∈（π/2,π）,求sin（x+B）,cos（x-B）

Answer 1

sin（x+B)=sinxcosB+cosxsinB=(1/4)(-1/3)+(-√15/4)(2√2/3)=-(1+2√30)/12

cos(x-B)=cosxcosB+sinxsinB=(-√15/4)(-1/3)+(1/4)(2√2/3)=(√15+2√2)/12