Question

已知二次函數(shù)=²++（≠0）的圖象如圖所示,在下列五個(gè)結(jié)論中:
①2－＜0;②＜0;③;④－+＞0; ⑤4+2+＞0,錯(cuò)誤的個(gè)數(shù)有

A．1個(gè)

B．2個(gè)

C．3個(gè)

D．4個(gè)

Answer 1

B．

試題分析:①∵由函數(shù)圖象開(kāi)口向下可知,a＜0,由函數(shù)的對(duì)稱(chēng)軸x=﹣＞﹣1,故＜1,∵a＜0,∴b＞2a,所以2a﹣b＜0,①正確;
②∵a＜0,對(duì)稱(chēng)軸在y軸左側(cè),a,b同號(hào),圖象與y軸交于負(fù)半軸,則c＜0,故abc＜0;②正確;
③當(dāng)x=1時(shí),y=a+b+c＜0,③正確;
④當(dāng)x=﹣1時(shí),y=a﹣b+c＜0,④錯(cuò)誤;
⑤當(dāng)x=2時(shí),y=4a+2b+c＜0,⑤錯(cuò)誤;
故錯(cuò)誤的有2個(gè)．
故選B．
考點(diǎn):二次函數(shù)圖象與系數(shù)的關(guān)系．