为什么x1-x2的绝对值=根号下（x1+x2）的平方-4x1x2,具体怎么推出来的啊,
因为（x1+x2）的平方-4x1x2=(x1的平方+x2的平方+2x1x2)-4x1x2=x1的平方+x2的平方-2x1x2=(x1-x2)的平方
绛旓細闊﹁揪鍏紡鐨勮繍鐢x1-x2鐨勭粷瀵瑰涓鍏冧簩娆℃柟绋嬩腑浠ｈ〃涓や釜鏍瑰湪鏁拌酱涓婄殑璺濈锛屽洜涓猴紙X1+X2锛塣2-4X1*X2=X1^2+X2^2-2X1*X2=(x1-x2)^ 2鎵浠ュ氨鐢▅(x1-x2)|=(锛圶1+X2锛塣2-4X1*X2)^1/ 2 鍐嶇粨鍚堥煢杈惧畾鐞嗘潵姹傚嚭x1-x2鐨勭粷瀵瑰 ...
绛旓細瑙:鈭祒1锛寈2婊¤冻缁濆鍊锛X1-X2锛=鈭5,鈭(x1-x2)^2=5,鈭祒1.x2骞冲潎鏁版槸x=(x1+x2)/2.鈭存柟宸=[(x1-x)^2+(x2-x)^2]/2 =[(x1-x2)^2/4+(x2-x1)^2/4]/2 =[2(x1-x2)^2/4]/2 =(x1-x2)^2/4 =5/4
绛旓細鎬ユ眰!!涓轰粈涔坸1-x2鐨勭粷瀵瑰=鏍瑰彿涓(x1+x2)鐨勫钩鏂-4x1x2涓昏鏄牴鍙蜂笅鐨勯儴鍒嗗叿浣撴槸鎬庝箞鏉ョ殑,璋㈣阿鍟!1涓洖绛 #鐑# 鑱屽満涓婂彈濮斿眻瑕佷笉瑕佷负鑷繁瑙ｉ噴?feng123h0 2013-12-21 路 TA鑾峰緱瓒呰繃6125涓禐 鐭ラ亾澶ф湁鍙负绛斾富 鍥炵瓟閲:2849 閲囩撼鐜:100% 甯姪鐨勪汉:2159涓 鎴戜篃鍘荤瓟棰樿闂釜浜洪〉 鍏虫敞 ...
绛旓細x1➖x2鐨勭粷瀵瑰鏄浠涔 =鈭(x1-x2)²=鈭歔(x1+x2)²-4x1x2]=鈭(b²-4ac) /|a|
绛旓細|x1-x2|銆傛牴鎹浉鍏宠祫鏂欐煡璇紝x1-x浜岀殑缁濆鍊绛変簬|x1-x2|锛岀粷瀵瑰兼槸鎸囦竴涓暟鍦ㄦ暟杞翠笂鎵瀵瑰簲鐐瑰埌鍘熺偣鐨勮窛绂伙紝鐢ㄢ渱|鈥濇潵琛ㄧず銆
绛旓細鑰岋紙x1-x2)²=(x1+x2)²锛4x1*x2 ( 娉ㄦ剰涓嬮潰杩欎竴姝ワ紝鏄妸x1-x2褰撲綔鏈煡鏁板埄鐢ㄧ洿鎺ュ紑骞虫柟娉曟潵姹傜殑,)鏍规嵁骞虫柟鏍圭殑瀹氫箟鍙緱 x1-x2=卤鈭歔(x1+x2)²锛4 x1*x2]=卤鈭歔(-3/2)²锛4锛堬紞1/2锛塢=卤鈭17/2 2,鑷充簬涓轰粈涔鈥滈殢渚垮姞缁濆鍊鈥濄傞鍏堬紝浣犵殑寮忓瓙鏄笉...
绛旓細|x1-x2| =鈭(x1-x2)²=鈭歔(x1+x2)²-4x1x2]
绛旓細y=ax^2+bx+c, 鐢▁=0浠ｅ叆锛屽緱y=0, 鎵浠ヤ簩娆″嚱鏁扮殑鍥捐薄涓巠 杞翠氦浜庣偣(0,c)姹傛牴鍏紡x1,x2=(-b+-V(b^2-4ac))/2a 涓嬮潰鐢╒鈻充唬鏇縑(b^2-4ac)鎶婃眰鏍瑰叕寮忎唬鍏x1-x2|=|(-b+V鈻)/2a-(-b-V鈻)/2a=|2V鈻/2a|=|V鈻/a|=|V鈻硘/|a|(鍒嗗瓙缁濆鍊鍐呮槸姝ｇ殑锛屾墍浠ョ粷瀵瑰...
绛旓細鐢辨牴涓庣郴鏁扮殑鍏崇郴鐭ワ細x1+x2=1锛寈1*x2=-1 |x1-x2|=鈭(x1-x2)^2=|=鈭歔(x1+x2)^-4x1*x2]=鈭5
绛旓細缁濆鍊糥1-X2=鏍瑰彿涓嬶紙X1-X2锛塣2=鏍瑰彿涓媨(X1+X2)^2-4X1*X2}=鏍瑰彿涓(a^2-4b锛
