求人教版数学必修四P137 13化简的（7）——（9）题 （7）sin(a+b)cos(γ-b)-cos(b+a)sin(b-γ)（8）sin(a-b)cos(b-γ)-cos(a-b)sin(γ-b)（9）tan5π/4+tan5π/12 / 1-tan5π/12
网友回答
(7) =sin(a+b)cos(b-y)-cos(a+b)sin(b-γ)=sin(a+b-(b-y))=sin(a-y) ;
(8) =sin(a-b)cos(y-b)-cos(a-b)sin(γ-b) =sin(a-b-(y-b))=sin(a-y) ;
(9) =(tanπ/4+tan5π/12) /( 1-tan5π/12)=tan(π/4+5π/12)=tan(8π/12)=tan(2π/3)=根号3 ；