Toán Lớp 8: b1:Tính a)5x^2.(x^3+x-7) b)(x^2+2xy-3).(-xy) c)(5x-2y)(x^2-x+1) d)x.(x^2+x+1)-x^2(x+1)-x+5 bài2:Phân tích thành nhân tử a)100x-5xy b)1

Question

Toán Lớp 8:  b1:Tính a)5x^2.(x^3+x-7) b)(x^2+2xy-3).(-xy) c)(5x-2y)(x^2-x+1) d)x.(x^2+x+1)-x^2(x+1)-x+5 bài2:Phân tích thành  nhân tử a)100x-5xy b)14x^2y-21xy^2 +28x^2y^2 c)3(x-y)-5x(y-x) d) 5x2 (x-2y)-15x(x-2y) e)x^2-y^2 +4x +4  f)x^3 +3x-4x-12

truongthanhhung · Answer

B&agrave;i 1  :  a)5x&sup2;.(x&sup3;+x-7)   = 5x^5 + 5x&sup3;- 35x&sup2;   b)  ( x&sup2;+2xy-3 ).( - xy )     = -x&sup3;y - 2x&sup2;y&sup2; + 3xy     c) ( 5x-2y )( x&sup2;- x +1 )     = 5x&sup3; - 5x&sup2; + 5x - 2x&sup2;y + 2xy - 2y     d) x.(x&sup2;+x+1)-x&sup2;(x+1)-x+5     = x&sup3; + x&sup2;- x - x&sup3; - x&sup2; - x + 5 = -2x + 5      B&agrave;i 2:   a) 100x - 5xy  = 5x ( 20 - y )   b) 14 x&sup2;y - 21 xy&sup2; + 28 x&sup2;y&sup2;   = 7xy . ( 2x - 3y + 4xy) c) 3( x-y ) - 5x ( y-x ) = ( x-y ) ( 3+5x ) d)  5x&sup2; (x-2y)-15x(x-2y)  = ( 5x&sup2; -15x ) ( x-2y ) =5x - ( x-3 ) ( x-2y )   e) x&sup2;-y&sup2; +4x +4       f) x&sup3;+3x-4x-12 ( 2 c&acirc;u n&agrave;y kh&ocirc;ng ph&acirc;n t&iacute;ch đc nha )

kimlien · Answer

1)   a) 5x^2 ( x^3 + x - 7 )   = 5x^5 + 5x^3 - 35x^2   b) ( x^2 + 2xy - 3 )(-xy)   = -x^3 y - 2x^2 y^2 + 3xy   c) ( 5x - 2y )(x^2 - x + 1 )   = 5x^3 - 5x^2 + 5x - 2x^2 y + 2xy - 2y   d) x( x^2 + x - 1 ) - x^2( x + 1 ) - x + 5   = x^3 + x^2 - x - x^3 - x^2 - x + 5   = -2x + 5   2)   a) 100x - 5xy = 5x(20 - y )   b) 14x^2 y - 21xy^2 + 28x^2 y^2 = 7xy(2x - 3y + 4xy )   c) 3(x-y) - 5x(y-x) = (x-y)( 3 + 5x )   d) 5x^2( x - 2y ) - 15x( x - 2y ) = ( 5x^2 - 15x)(x-2y) = 5x(x - 3)(x - 2y )   e) x^2 - y^2 + 4x + 4Kh&ocirc;ng thẻ ph&acirc;n t&iacute;ch .   Sửa đề : x^2 - y^2 + 4x + 4y = ( x - y )(x+y ) + 4( x + y  ) = (x+y)(x-y+4)   f) x^3 + 3x - 4x - 12 ( Kh&ocirc;ng thể ph&acirc;n t&iacute;ch )