Toán Lớp 8: a)5x(1/5x-2)+3(6-1/3x²)=12 b)7x(x-2)-5(x-1)=7x²+3 c) 2x²+3(x-1)(x+1)=5x(x+1)

Question

Toán Lớp 8:  a)5x(1/5x-2)+3(6-1/3x²)=12 b)7x(x-2)-5(x-1)=7x²+3 c) 2x²+3(x-1)(x+1)=5x(x+1)

giahan44 · Answer

Giải đáp:       Lời giải và giải thích chi tiết:    a, 5x(1/5 x - 2) + 3(6 - 1/3 x^2) = 12   5x . 1/5 x + 5x.(-2) + 3.6 + 3.(-1/3 x^2) = 12   x^2 - 10x + 18 - x^2 = 12   -10x + 18 = 12   -10x = 12 - 18   -10x = -6   x = (-6)/(-10)   x = 3/5   Vậy x = 3/5   b, 7x(x - 2) - 5(x - 1) = 7x^2 + 3   &hArr; 7x.x + 7x.(-2) + (-5).x + (-5).(-1) = 7x^2 + 3   &hArr; 7x^2 - 14x - 5x + 5 - 7x^2 - 3 = 0   &hArr; (7x^2 - 7x^2) + (-14x - 5x) + (5 - 3) =0   &hArr; -19x + 2 = 0   &hArr; -19x = -2   &rArr; x = (-2)/-19   &rArr; x = 2/19   Vậy x = 2/19   c, 2x^2 + 3(x - 1)(x + 1) = 5x(x + 1)   &hArr; 2x^2 + 3(x^2 - 1^2) - 5x(x + 1) = 0   &hArr; 2x^2 + 3x^2 - 3 - 5x^2 - 5x = 0   &hArr; (2x^2 + 3x^2 - 5x^2) - 3 - 5x = 0   &hArr; -5x - 3 = 0   &hArr; -5x = 3   &rArr; x = -3/5   Vậy x = -3/5

thanhbinh2k5 · Answer

Lời giải và giải thích chi tiết:   a) 5x(1/5x-2)+3(6-1/3x&sup2;)=12     &hArr;x&sup2;-10x+18-x&sup2;=12     &hArr;-10x+18=12     &hArr;-10x=-6     &hArr;x=3/5     b)7x(x-2)-5(x-1)=7x&sup2;+3     &hArr;7x&sup2;-14x-5x+5=7x&sup2;+3     &hArr;7x&sup2;-19x-7x&sup2;=3-5     &hArr;-19x=-2     &hArr;x=2/19     c)2x&sup2;+3(x-1)(x+1)=5x(x+1)     &hArr;2x&sup2;+3(x&sup2;-1)=5x&sup2;+5x     &hArr;2x&sup2;+3x&sup2;-3-5x&sup2;-5x=0     &hArr;-5x=3     &hArr;x=-3/5     Cho m&igrave;nh xin ctlhn nha<3     M&igrave;nh cảm ơnn