特称命题:是否存在a,b使 (1)sin(a-b)=sina-sinb,( 2 )cos(a

问题描述:

特称命题:是否存在a,b使 (1)sin(a-b)=sina-sinb,( 2 )cos(a
(1)sin(a-b)=sina-sinb,( 2 )cos(a-b)=cosa-cosb
2个命题都正确吗?

显然是存在的,对a=0,b=π/3,便有
sin(0-π/3)=sin0-sinπ/3
cos(0-π/3)=cos0-cosπ/3