Toán Lớp 8: Tìm x,biết: a)x(x+1)-5(x+1)=0 b)5(x-1)^2-(x-1)(x+1)=0 c)25-x^2=0 d)2x^2-5x+3=0

Question

Toán Lớp 8:  Tìm x,biết: a)x(x+1)-5(x+1)=0 b)5(x-1)^2-(x-1)(x+1)=0 c)25-x^2=0 d)2x^2-5x+3=0

tonhu12 · Answer

a)  x(x+1)-5(x+1)=0     &hArr; (x+1)(x-5)=0     &rArr; x+1=0    hoặc  x-5=0     &rArr;     x=-1   hoặc     x=5     Vậy x &isin; {-1;5}      b)  5(x-1)&sup2;-(x-1)(x+1)=0     &hArr; (5x-5)(x-1)-(x-1)(x+1)=0     &hArr;           (x-1)(5x-5-x-1)=0     &hArr;                  (x-1)(4x-6)=0     &rArr; x-1=0  hoặc  4x-6=0     &hArr;    x=1  hoặc  4x=6     &hArr;    x=1  hoặc    x=6/4=3/2     Vậy x &isin; {1;3/2}     c)  25-x&sup2;=0   &hArr; (5+x)(5-x)=0   &rArr; 5+x=0   hoặc  5-x=0   &hArr;     x=-5 hoặc     x=5   Vậy x &isin; {5;-5}    d)  2x&sup2;-5x+3=0   &hArr;    2x&sup2;-2x-3x+3=0   &hArr; 2x(x-1)-3(x+1)=0   &hArr;       (x-1)(2x-3)=0   &rArr; x-1=0  hoặc  2x-3=0   &hArr;    x=1  hoặc     2x=3   &hArr;    x=1  hoặc       x=3/2   Vậy x &isin; {1;3/2}      Ch&uacute;c bạn học tốt, cho m&igrave;nh CTLHN+5*+tim nha!!!

diemchau · Answer

a)x(x+1)-5(x+1)=0 <=> x^2 +x-5(x+1)=0 <=> x^2 +x-5x-5=0 <=> (x-5)(x+1)=0 TH1: x-5=0 <=> x=5 TH2: x+1=0 <=> x=-1 => x∈{5;-1} b) 5(x-1)^2 -(x-1)(x+1)=0 <=> 4x^2 -10x+6=0 <=> 2(2x-3)(x-1)=0 TH1: 2x-3=0 <=> 2x=3 <=> x=3/2 TH2: x-1=0 <=> x=1 => x∈{ 3/2 ; 1} c) 25-x^2 =0 <=> x^2 =25 <=> x^2 =5^2 <=> x=±5 d) 2x^2 -5x+3=0 <=> (2x-3)(x-1)=0 TH1: 2x-3=0 <=> 2x=3 <=> x=3/2 TH2: x-1=0 <=> x=1 => x∈{ 3/2 ; 1 }