Toán Lớp 8: Bài 3: Tìm x biết: a) 3(2x – 1) – 5(x – 3) + 6(3x – 4) = 24 b) 2x(5 – 3x) + 3x( 2x – 5) – 3(x – 7) = 3 c) 3x( x + 1) – 2x( x + 2) = 1

Question

Toán Lớp 8:  Bài 3: Tìm x biết: a) 3(2x – 1) – 5(x – 3) + 6(3x – 4) = 24  b) 2x(5 – 3x) + 3x( 2x – 5) – 3(x – 7) = 3  c) 3x( x + 1) – 2x( x + 2) = 1 – x  d) 2x2 + 3(x2 – 1) = 5x(x +1)  e) ( 3x – 1)(2x + 7) – ( x + 1)(6x – 5) = 16  f) (10x + 9)x – (5x + 2)(2x + 3) – 8 = 0  g) ( 3x – 5)(7 – 5x) + ( 5x + 2)(3x – 2) = 2  h) (x – 3)(x +7) – (x + 5)(x – 1) = 0

thanhtung · Answer

a)3(2x-1)-5(x-3)+6(3x-4)=24   &hArr;6x-3-5x+15+18x-24=24   &hArr;(6x-5x+18x)+(-3+15-24)=24   &hArr;19x-12=24   &hArr;19x=24+12   &hArr;19x=36   &hArr;x=36/19   Vậy x=36/19   b)2x(5-3x)+3x(2x-5)-3(x-7)=3   &hArr;10x-6x&sup2;+6x&sup2;-15x-3x+21=3   &hArr;(10x-15x-3x)+(-6x&sup2;+6x&sup2;)+21=3   &hArr;-8x+21=3   &hArr;-8x=3-21   &hArr;-8x=-18   &hArr;x=18/8   &hArr;x=9/4   Vậy x=9/4   c)3x(x+1)-2x(x+2)=1-x   &hArr;3x&sup2;+3x-2x&sup2;-4x=1-x   &hArr;(3x&sup2;-2x&sup2;)+(3x-4x)=1-x   &hArr;x&sup2;-x=1-x   &hArr;x&sup2;-x+x=1   &hArr;x&sup2;=1   &hArr;x=&plusmn;1   Vậy x=1 hoặc x=-1   d)2x&sup2;+3(x&sup2;-1)=5x(x+1)   &hArr;2x&sup2;+3x&sup2;-3=5x&sup2;+5x   &hArr;5x&sup2;-3=5x&sup2;+5x   &hArr;5x&sup2;-5x&sup2;-5x=3   &hArr;-5x=3   &hArr;x=-3/5   Vậy x=-3/5   e)(3x-1)(2x+7)-(x+1)(6x-5)=16   &hArr;6x&sup2;+21x-2x-7-(6x&sup2;-5x+6x-5)=16   &hArr;6x&sup2;+21x-2x-7-6x&sup2;+5x-6x+5=16   &hArr;(6x&sup2;-6x&sup2;)+(21x-2x+5x-6x)+(-7+5)=16   &hArr;18x-2=16   &hArr;18x=16+2   &hArr;18x=18   &hArr;x=18:18   &hArr;x=1   Vậy x=1   f)(10x+9)x-(5x+2)(2x+3)-8=0   &hArr;10x&sup2;+9x-(10x&sup2;+15x+4x+6)-8=0   &hArr;10x&sup2;+9x-10x&sup2;-15x-4x-6-8=0   &hArr;(10x&sup2;-10x&sup2;)+(9x-15x-4x)-(6+8)=0   &hArr;-10x-14=0   &hArr;-10x=14   &hArr;x=-14/10   &hArr;x=-7/5   Vậy x=-7/5   g)(3x-5)(7-5x)+(5x+2)(3x-2)=2   &hArr;21x-15x&sup2;-35+25x+15x&sup2;-10x+6x-4=2   &hArr;(21x+25x-10x+6x)+(-15x&sup2;+15x&sup2;)-(35+4)=2   &hArr;42x-39=2   &hArr;42x=2+39   &hArr;42x=41   &hArr;x=41/42   Vậy x=41/42   h)(x-3)(x+7)-(x+5)(x-1)=0   &hArr;x&sup2;+7x-3x-21-(x&sup2;-x+5x-5)=0   &hArr;x&sup2;+7x-3x-21-x&sup2;+x-5x+5=0   &hArr;(x&sup2;-x&sup2;)+(7x-3x+x-5x)+(-21+5)=0   &hArr;0x-16=0   &hArr;0x=16(v&ocirc; l&iacute;)   Vậy phương tr&igrave;nh v&ocirc; nghiệm