Toán Lớp 8: Tìm x biết : a) ( x+1)(2x-3)-3.(x-2) = 2 . (x-1)^2 b ) 4 ( x+3)(3x-2)-3 (x-1)(4x-1)=-27

Question

Toán Lớp 8:  Tìm x biết :  a) ( x+1)(2x-3)-3.(x-2) = 2 . (x-1)^2  b ) 4 ( x+3)(3x-2)-3 (x-1)(4x-1)=-27

giahan44 · Answer

Giải đáp:    a, (x +1)(2x - 3) - 3(x - 2) = 2(x - 1)^2   &hArr; 2x^2 - 3x + 2x - 3 - (3x - 6) = 2(x^2 - 2x + 1)   &hArr; 2x^2 - 3x + 2x - 3 - 3x + 6 = 2x^2 - 4x + 2   &hArr; 2x^2 - 3x + 2x - 3 - 3x + 6 - 2x^2 + 4x - 2 = 0   &hArr; (2x^2 - 2x^2) + (-3x + 2x - 3x + 4x) + (-3 + 6 - 2) = 0   &hArr;  1 = 0 (v&ocirc; l&yacute;)   &rArr; x &isin; $ emptyset$   b, 4(x + 3)(3x - 2) - 3(x - 1)(4x - 1) = -27   &hArr; (4x + 12)(3x - 2)- 3(4x^2 - x - 4x + 1) = -27   &hArr; 12x^2 - 8x + 36x - 24 - 12x^2 + 3x + 12x - 3 + 27 = 0   &hArr; (12x^2 - 12x^2) + (-8x + 36x +  3x + 12x) + (- 24 - 3 + 27) = 0   &hArr; 43x = 0   &rArr; x = 0

thanhbinh2k5 · Answer

Giải đáp: a) ( x+1)(2x-3)-3.(x-2) = 2 . (x-1)^2 <=> 2x² - 3x + 2x - 3 - 3x + 6 = 2x² - 4x + 2 <=> 2x² - 3x + 2x - 3 - 3x + 6 - 2x² + 4x - 2= 0 <=> 1=0 ( vô lí) Vậy S=∅ b) 4 ( x+3)(3x-2)-3 (x-1)(4x-1)=-27 <=> (4x + 12)(3x-2) - ( 3x - 3)(4x-1)= -27 <=> 12x² - 8x + 36x - 24 - 12x² + 3x + 12x -3 + 27=0 <=>43x= 0 <=> x=0 Vậy S={0}