Question

已知A、B、C为△ABC的三个内角。求证:sin(A+B)/2=cosC/2，cos(A+B)/2=sinC/2，sin(A+B)=sinC，cos(A+B)...

已知A、B、C为△ABC的三个内角。求证:sin(A+B)/2=cosC/2，cos(A+B)/2=sinC/2，sin(A+B)=sinC，cos(A+B)=-cosC，tan(A+B)=-tanC。填空:sin2(A+B)=?cos2(A+B)=?tan2(A+B)=?

Answer 1

sin(A+B)/2=sin(180-c)/2=sin(90-c/2)=cosC/2 ，
cos(A+B)/2=cos(180-c)/2=cos(90-c/2)=sinC/2，
sin(A+B)=sin(180-c)=sinC，
cos(A+B)=cos(180-c)=-cosC，
tan(A+B)=tan(180-c)=-tanC。

填空:
sin2(A+B)=sin2(180-c)=sin(360-2c)=-sin2c
cos2(A+B)=cos2(180-c)=cos(360-2c)=cos2c
tan2(A+B)=tan2(180-c)=tan(360-2c)=-tan2c

Answer 2

sin(A+B)/2=sin(π-c)/2=cosC/2 ，
cos(A+B)/2=cos(π-c)/2=sinC/2，
sin(A+B)=sin(π-c)=sinC，
cos(A+B)=cos(π-c)=-cosC，
tan(A+B)=tan(π-c)=-tanC。

sin2(A+B)=sin2(π-c)=-sin2c
cos2(A+B)=cos2(π-c)=cos2c
tan2(A+B)=tan2(π-c)=tan2c

Answer 3

最烦数学

Answer 4

你丫的，滚一边去