下列命题中真命题的是( )。
①若a+b>0且ab>0,则a>0且b<0.
②若a>b且ab>0,则a>b>0
③在同一平面内,垂直于同一直线的两直线平行。
④一个锐角的补角比它的余角小90°。
下列命题中真命题的是( ) ①若a+b>0且ab>0,则a>0且b<0. ②若a>b且ab>0,则a>b>0 ③在同
答案:4 悬赏:70
解决时间 2021-03-06 19:58
- 提问者网友:江山如画
- 2021-03-06 07:37
最佳答案
- 二级知识专家网友:心痛成瘾
- 2021-03-06 08:00
假,假,真,假
①若a+b>0且ab>0,则a>0且b<0.
假,原因:ab>0,说明a、b同号,所以已知成立,则结论不成立
②若a>b且ab>0,则a>b>0
假,原因:ab>0,说明a、b同号;若a、b同为正,则a>b>0,若a、b同为负,则应为b<a<0
③在同一平面内,垂直于同一直线的两直线平行。
真(前提:同一平面内的两直线,通常是指不重合的两直线;该结论,对于空间则不一定成立)
④一个锐角的补角比它的余角小90°。
假,令0<A<90°,则其补角为90°<B=180°-A<180°,其余角为0<C=90°-A<90°
则其补角与余角的差为:B-C=(180°-A)-(90°-A)=90°
因此,应该是“一个锐角的补角比它的余角小90°。”
①若a+b>0且ab>0,则a>0且b<0.
假,原因:ab>0,说明a、b同号,所以已知成立,则结论不成立
②若a>b且ab>0,则a>b>0
假,原因:ab>0,说明a、b同号;若a、b同为正,则a>b>0,若a、b同为负,则应为b<a<0
③在同一平面内,垂直于同一直线的两直线平行。
真(前提:同一平面内的两直线,通常是指不重合的两直线;该结论,对于空间则不一定成立)
④一个锐角的补角比它的余角小90°。
假,令0<A<90°,则其补角为90°<B=180°-A<180°,其余角为0<C=90°-A<90°
则其补角与余角的差为:B-C=(180°-A)-(90°-A)=90°
因此,应该是“一个锐角的补角比它的余角小90°。”
全部回答
- 1楼网友:而你却相形见绌
- 2021-03-06 11:05
c
你只要知道一点某命题是正确的话,那么原来命题的逆否命题也正确
很显然,原命题的逆否命题是c选项,那么c就是正确的
不懂追问哈,希望能被采纳^^
- 2楼网友:我的任性你不懂
- 2021-03-06 10:16
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- 3楼网友:蜜罐小熊
- 2021-03-06 09:05
1错ab大于0,a,b要同号 2错.a大于b 可以两个都为负数 3. 对 4. 错 小字改为大
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