Question

请问这道题咋解，谢谢了

Answer 1

如果x1<1<x2，
则x=1时，x²+x+a<0，
a<-x²-x=-1²-1=-2，即a<-2

Answer 2

1.原式=(sina/cosa)乘以 sina 乘以cosa =sina^2 2.原式=cos^2(a)-tana/sina =cos^2(a)-1/cosa =(cos^3-1)/cosa 补充:cos(α-π/2)=sina sin(5π/2+α)=sin(π/2-a)=cosa sin(α-2π)=sina cos(2π--α)=)=cos(-α)=cosa