1）sin(180°+a)*cos(360°+a)/[cot(-a-180°)*sin(-180°-a)]+sin(a+180°)*cos(-a)/cot(a+180°)
=-sinacosa/[cot(-a)*sina]+[-sina*cosa]/cota
=sina-sin²a
2）cot765°-tan675°+cot(-690°)-tan(-300°)
=cot(4*180°+45°)-tan(4*180°-45°)+cot(-4*180°+30°)-tan(-2*180°+60°)
=1-（-1）+cot30°-tan60°
=2
3）cos(9π/4)+cot(-7π/6)+sin(-π)+cot(-5π/6)
=cos(2π+π/4)+cot(-π-π/6)+0+cot(-π+π/6)
=cos(π/4)+cot(-π/6)+cot(π/6)
=cos(π/4)=√2/2(√表示根号)
4）cos(π/6-A)=cos(2π/3-π/2-A)=sin(2π/3-A)=M
5）F(x)=sin(πx)(x＜0)
你这道题x＜0和x＞0之间的题写错了或者没写全吧