Toán Lớp 8: giúp mk vs lm ơn 1. Tìm x biết a)x ² +4x-5=0 b) (x-3) ²+x ²-9=0

Question

Toán Lớp 8:  giúp mk vs   lm ơn           1. Tìm x biết a)x ² +4x-5=0 b) (x-3) ²+x ²-9=0

kymmailien · Answer

&hArr;Giải đáp:       Lời giải và giải thích chi tiết:    a,x&sup2;+4x-5=0   &hArr;x&sup2;-x+5x-5=0   &hArr;x(x-1)+5(x-1)=0   &hArr;(x+5)(x-1)=0   &hArr; ( left[  begin{array}{l}x+5=0  x-1=0 end{array}  right. )    &hArr; ( left[  begin{array}{l}x=-5  x=1 end{array}  right. )    b,(x-3)&sup2;+x&sup2;-9=0   &hArr;(x-3)(x-3)+(x-3)(x+3)=0   &hArr;(x-3)(x-3+x+3)=0   &hArr;(x-3)2x=0   &hArr;  ( left[  begin{array}{l}x-3=0  2x=0 end{array}  right. )    &hArr; ( left[  begin{array}{l}x=3  x=0 end{array}  right. )    cho mk c&acirc;u trẻ lời hay nhất nh&aacute;

mytamhoang · Answer

Lời giải:     a)   x^(2)+4x-5=0   &hArr;x^(2)+5x-x-5=0   &hArr;x(x+5)-(x+5)=0   &hArr;(x+5)(x-1)=0   $&hArr; left[ begin{matrix}x+5=0   x-1=0 end{matrix} right.$   $&hArr; left[ begin{matrix}x=-5   x=1 end{matrix} right.$   Vậy x&isin;{-5;1}   b)   (x-3)^(2)+x^(2)-9=0   &hArr;(x-3)^(2)+(x-3)(x+3)=0   &hArr;(x-3)(x-3+x+3)=0   &hArr;(x-3).2x=0   $&hArr; left[ begin{matrix}x-3=0   2x=0 end{matrix} right.$   $&hArr; left[ begin{matrix}x=3   x=0 end{matrix} right.$   Vậy x&isin;{3;0}