Toán Lớp 8: Tìm x biết: a, 6x^2-19x+15=0 b, 4x^3-11x^2+14x-6=0

Question

Toán Lớp 8:  Tìm x biết: a, 6x^2-19x+15=0 b, 4x^3-11x^2+14x-6=0

huongtructram · Answer

Giải đáp:       Lời giải và giải thích chi tiết:   a) 6x&sup2; - 19x + 15 = 0   &hArr; 6x&sup2; - 9x - 10x + 15 = 0    &hArr; 3x(2x - 3) - 5(2x - 3) = 0   &hArr; (3x - 5)(2x - 3) = 0   &hArr;  ( left[  begin{array}{l}3x-5=0  2x-3=0 end{array}  right. )    &hArr;  ( left[  begin{array}{l}x= frac{5}{3}  x= frac{3}{2} end{array}  right. )   b) 4x&sup3; - 11x&sup2; + 14x - 6 = 0   &hArr; 4????&sup3; &minus; 8????&sup2; + 8???? &minus; 3????&sup2; + 6???? &minus; 6 = 0   &hArr; (4????&sup3; &minus; 8????&sup2; + 8????) &minus; (3????&sup2; - 6???? + 6) = 0   &hArr; 4???? (????&sup2; &minus; 2???? + 2) &minus; 3(????&sup2; &minus; 2???? + 2) = 0   &hArr; (4???? &minus; 3)(????&sup2; &minus; 2???? + 2) = 0   M&agrave; x&sup2; - 2x + 2 = x&sup2; - 2x + 1 + 1 = (x - 1)&sup2; + 1 > 0    &rArr; 4x - 3 = 0   &rArr; x =

diemchau · Answer

Giải đáp:   a, 6x&sup2;-19x+15 = 0   &hArr; 6x&sup2;-9x-10x+15 = 0   &hArr;(6x&sup2;-9x) - (10x-15) = 0   &hArr; 3x(2x-3) - 5(3x-3) = 0   &hArr; (2x-3)(3x-5)=0   &rArr; ( left[  begin{array}{l}2x-3=0  3x-5=0 end{array}  right. )    &rArr; ( left[  begin{array}{l}x= frac{3}{2}  x= frac{5}{3} end{array}  right. )      b, 4x&sup3;-11x&sup2;+14x-6 = 0   &hArr;4????&sup3;&minus;8????&sup2;+8????&minus;3????&sup2;+6????&minus;6 = 0   &hArr;(4????&sup3;&minus;8????&sup2;+8????)&minus;(3????&sup2;-6????+6) = 0   &hArr;4????(????&sup2;&minus;2????+2)&minus;3(????2&minus;2????+2)= = 0   &hArr;(4????&minus;3)(????&sup2;&minus;2????+2) = 0   &rArr; ( left[  begin{array}{l}4x-3=0  x&sup2;-2x+2=0 end{array}  right. )   &rArr;4x-3=0   &rArr;x=$ frac{3}{4}$