câu 1:
a) 4x( 5x + 9 )
= 4x5x + 4x9
= 20x2+36x
b) (3x - 2) ( x+7 )
= 3xx + 3x7 - 2x - 2 . 7
= 3x2+ 21x - 2x - 14
= 3x2 +19x - 14
c) (2x- 5 )(x2-7x + 4 )
= 2xx2 - 2x7x + 2x4 - 5x2 +5 . 7x - 5.4
= 2x3- 14x2+8x - 5x 2+ 35x - 20
= 2x3+ ( - 14x2- 5x2 )+(8x+35x) - 20
= 2x3 - 9x2 + 43x - 20
Câu 2 :
a) (5x - 3x)2
= (5x)2 - 2.5x3y + (3y)2
= 25x2 - 30xy +9y
b) (2x - 5)(2x + 5)
= (2x)2 - 52
= 4x2 - 25
c) (3x - 7y)3
= ( 3x)3 - 3(3x)27y + 3.3x(7y)2 - (7y)2
= 27x3 - 189x2y + 441xy2- 343y3
d) (x+5)(x2-5x+25)
= (x+5)(x2-5x+52)
= x3+53
= x3+125
Câu 3 :
a) 25x-30x2
= 5.5x-5.6xx
= 5x(5-6x)
b) 8x(x+4y)+16(x+4y)
= (x+4y)(8x+16)
c) 24x8y7 -15x6y5+18x6y3
= 3.8x6x2y3y4-3.5x6y3y2+3.6x6y3
= 3x6y3(8x2y4-5y2+6)