给出下列4个命题：是全称命题的是_1①a→⊥b→⇔a→·b→=0 ；②矩形都不是梯形；③∃x,y&#871_刷题宝

题干

给出下列4个命题：是全称命题的是____

①a→⊥b→⇔a→·b→=0 ；

②矩形都不是梯形；

③∃x,y∈R,x+y≤1 ；

④任意互相垂直的两条直线的斜率之积等于－1。其中全称命题是。

上一题下一题 0.0难度选择题更新时间:2017-05-06 09:43:18

答案(点此获取答案解析）

①②④

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