... thừa số bằng 0 ) a) x 2 - x = x.x - x= x(x -1 ) b) 5x 2 (x-2y )-1 5x(x-2y)=5x.x(x-2y )- 3.5x(x-2y) = 5x(x- 2y)(x- 3) c)3(x-y )-5 x(y- x)=3(x- y)+5x(x- y) = (x- y)(3 + 5x) VD: -5 x(y-x) =-( -5 x) [-( y-x)] ... tử. b) 10x-25-x 2 = -( x 2 -2 .5x+5 2 ) = -( x-5) 2 = -( x-5)(x-5) c) 8x 3 - 1 8 = (2x) 3 -( 1 2 ) 3 = (2x- 1 2 )(4x 2 +x+ 1 4 ) d) 1 25 x 2 -6 4y 2 = ( 1 5 x) 2 -( 8y) 2 = ( 1 5 x-8y)( 1 5 x+8y) Bài ... -1 5-1 5 = -3 0 c) Khi x = - 15 thì A = 15 -1 5 = 0 d) Khi x = 0,15 thì A = - 0,1 5-1 5 = - 15,15 3) Chữa bài 13 (sgk) Tìm x biết: (12x-5)(4x-1)+(3x-7)( 1-1 6x) = 81 (48x 2 - 12x - 20x +5) ( 3x + 48x...