问题
选择题
命题“∃(x,y),x,y∈R,2x+3y+3<0”的否定是( )
A．∃(x,y),x,y∈R,2x+3y+3>0
B．∃(x,y),x,y∈R,2x+3y+3≥0
C．∀(x,y),x,y∈R,2x+3y+3≥0
D．∀(x,y),x,y∈R,2x+3y+3>0
答案
答案：C
(x,y)的否定是
(x,y),2x+3y+3<0的否定是2x+3y+3≥0,故选C.
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