7.
a. ( x2 - 2x + 1 ) . ( x-1 ) = (x-1) . ( x2 - 2x + 1 )
= x.x2 -x . 2x + x.1 - 1 . x2 + 1. 2x - 1.1
= x3 - 2x2 + x - x2 + 2x - 1
= x3 - 3x2 + 3x - 1 .
b. ( x3 -2x2 + x - 1 ) . ( 5.x ) = ( 5 - x ) . ( x3 - 2x2 + x - 1 )
= 5. x3 - 5. 2x2 + 5.x - 5.1 - x . x3 + x . 2x2 - x . x - x.1
= 5x3 - 10x2 + 5x - 5 - x4 + 2x3 - x2 - x
= 7x3 - 11x2 + 4x -5 .
8.
a . ( x2y2 - 1/2xy + 2y ) . ( x-2y) = ( x-2y) . ( x2y2 - 1/2xy + 2y )
= x. x2y2 - x . 1/2xy + x.2y - 2y . x2y2 + 2y . 1/2xy - 2y.2y
= x3y2 - 1/2x2y + 2xy - 2x2y3 + xy2 - 4y2
b. ( x2 - xy + y2 ) . ( x + y )= ( x+y) . ( x2 - xy + y2 )
= x . x2 - x . xy + x . y2 + y.x2 - y . xy + y . y2
= x3 - x2y + xy2 + x2y - xy2 + y3
= x2 + y3 .
9.
Gía trị của x và y | Gía trị của biểu thức ( x-y) . ( x2 + xy + y2 ) |
x= -10 , y=2 |
( -10 - 2 ) . ( -102 + -10 . 2 + 22 ) = -12 . -116 = -128 |
x=-1 , y = 0 |
( -1 -0 ) . ( -12 + -1 . 0 + 02 ) = -1 . -1 = 1 |
x=2 , y = -1 |
( 2+1 ) . ( 22 + 2 . ( -1) + ( -1 )2 ) = 3.4 = 12 |
x= 0,5 , y = 1,25 |
( 0,5 - 1,25 ) ( 0, 52 + 0,5 . 1,25 + 1,252 ) = -0,75 . 39/16 = -117/64 |
10.
a. ( x2 - 2x + 3 ) . ( 1/2x - 5 ) = ( 1/2x - 5 ) . ( x2 - 2x + 3)
= 1/2x . x2 - 1/2x . 2x + 1/2x . 3 - 5 . x2 + 5 . 2x - 5.3
= 1/2x3 - 1x2 + 3/2 - 5x2 + 10x - 15
b. ( x2- 2xy + y2 ) . ( x - y ) = ( x-y ) . ( x2 - 2xy + y2 )
= x. x2 - x.2xy + x . y2 - y . x2 + y. 2xy - y . y2
= x3 - 2x2y + xy2 - x2y + 2xy2 - y3 .
Bài 11 mk chưa làm . Đợi xíu mk viết 12, 13 , 14 , 15 cho