Toán Lớp 8: bài 5: tìm x biết a)(x-2)(5x-1)-5x(x-3)=5 b)(4x+1)(x-3)-(x-7)(4x-1)=15 c)(3x-5)(x+1)-(3x-1)(x+1)=x-4 d)-4x mũ 2 (x-7)+4x(x mũ 2 -5)+28x

Question

Toán Lớp 8:  bài 5: tìm x biết a)(x-2)(5x-1)-5x(x-3)=5 b)(4x+1)(x-3)-(x-7)(4x-1)=15 c)(3x-5)(x+1)-(3x-1)(x+1)=x-4 d)-4x mũ 2 (x-7)+4x(x mũ 2 -5)+28x mũ 2 -13

dananhnhu2k4 · Answer

a)(x-2)(5x-1)-5x(x-3)=5   &hArr;5x&sup2;-x-10x+2-5x&sup2;+15x=5   &hArr;(5x&sup2;-5x&sup2;)+(-x-10x+15x)+2=5   &hArr;4x+2=5   &hArr;4x=5-2   &hArr;4x=3   &hArr;x=3/4   Vậy x=3/4   b)(4x+1)(x-3)-(x-7)(4x-1)=15   &hArr;4x&sup2;-12x+x-3-(4x&sup2;-x-28x+7)=15   &hArr;4x&sup2;-12x+x-3-4x&sup2;+x+28x-7=15   &hArr;(4x&sup2;-4x&sup2;)+(-12x+x+x+28x)-(3+7)=15   &hArr;18x-10=15   &hArr;18x=15+10   &hArr;18x=25   &hArr;x=25/18   Vậy x=25/18   c)(3x-5)(x+1)-(3x-1)(x+1)=x-4   &hArr;(x+1)[(3x-5)-(3x-1)]=x-4   &hArr;(x+1)(3x-5-3x+1)=x-4   &hArr;(x+1).(-4)=x-4   &hArr;-4x-4=x-4   &hArr;-4x-x=-4+4   &hArr;-5x=0   &hArr;x=0   Vậy x=0   d) đề thiếu dữ kiện