Thu gọn:
1) $2x^{2}$ +3(x-1)(x+2) -5x(x+1)
= $2x^{2}$ + 3($x^{2}$ +2x-x-2) - $5x^{2}$ -5x
=2$x^{2}$ + 3$x^{2}$ + 3x - 6 + 5$x^{2}$ -5x
= 2$x^{2}$ +3($x^{2}$+x-2) -5$x^{2}$ -5x
= 5$x^{2}$ -5$x^{2}$ + 3x - 5x -6
= -2x - 6
Thay x=1, ta có
-2 * 1 - 6= -2 - 6 = 8
b) 4$x^{2}$ - (x-1)(2x+5) +4(x-2)(x+1)
= 4$x^{2}$ - (2$x^{2}$ + 5x - 2x -5) + 4($x^{2}$ + x -2x -2)
= 4$x^{2}$ - 2$x^{2}$ -3x + 5 +4$x^{2}$ - 4x - 8
= 6$x^{2}$ - 7x - 3
Thay x= -1, ta có
6 .$(-1^{2})$ -7 . (-1) - 3
= 6 + 7 -3
= 10
Bài 1 trên
a) (-3x + 2)(4x+5) = -12x^2 - 15x + 8x +10
= -12x^2 - 7x + 10
b) (3-x+ 4x^2)(2-3x) = 6 - 9x - 2x + 3x^2 + 8x^2 - 12x^3
= -12x^3 + 11x^2 - 11x +6
c) ( 3x + 2)(x^2 - 5x +1) = 3x^3 - 15x^2 + 3x + 2x^2 - 10x + 2
= 3x^3 - 13x^2 - 7x +2
d) (x^2 -x +3)(-2x^2 +3)= -2x^4 + 3x^2 + 2x^3 - 3x - 6x^2 + 9
= -2x^4 + 2x^3 -3x^2 - 3x +9
Bài 1 dưới
a) (x-3)^2 = x^2 - 6x +9
b) (x-1/2)^2 = x^2 - x + 1/4
c) ( 5x - y)^2 = 25x^2 - 10xy + y^2
d) (10x^2 -3xy^2)^2 = 100x^4 - 60x^3y^2 + 9x^2y^4
Bài 2 dưới
a) x^2 - 4x + 4= (x-2)^2
b) x^2 - 10x +25 = (x-5)^2
