二次函数
一道二次函数的题目，如下图：<br />请指教<br /><br />[ 本帖最后由 xiaoyalin 于 2007-12-21 20:13 编辑 ]<br> 2个结论都正确。<br />1）<br />a+b+c=2<br />4a-2b+c<0<br />a+b+c<0<br /><br />消去c，得：b<-1,代入第一个不等式得：a<-1，<br /><br />2）判别式大于0，所以判别式－8a也大于0，第二个结论成立<br> a+b+c=2从哪得出？<br> <br><br>QUOTE:原帖由 xiaoyalin 于 2007-12-22 10:31 发表 <a href="http://bbs.pep.com.cn/redirect.php?goto=findpost&pid=3539654&ptid=346540" target="_blank"><img src="http://bbs.pep.com.cn/images/common/back.gif" border="0" onload="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" /></a><br />a+b+c=2从哪得出？ <br>写错了，应该是a-b+c=2<br> <br><br>QUOTE:原帖由 0574aaa 于 2007-12-21 20:44 发表 <a href="http://bbs.pep.com.cn/redirect.php?goto=findpost&pid=3538772&ptid=346540" target="_blank"><img src="http://bbs.pep.com.cn/images/common/back.gif" border="0" onload="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" /></a><br />2个结论都正确。<br />1）<br />a+b+c=2<br />4a-2b+c <br>如何消去c，得b<-1？<br />题目中还有条件没用，应该不会这么简单吧？<br /><br />[ 本帖最后由 xiaoyalin 于 2007-12-23 11:43 编辑 ]<br> a-b+c=2<br />代入<br />a+b+c<0<br /><br />即可得b<-1<br>页:
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