Đáp án:
a)2$x^{2}$ +3(x-1)(x+1)-5x(x+1)
2$x^{2}$ +3($x^{2}$ +x-x-1)-5$x^{2}$ -5x
2$x^{2}$ +3($x^{2}$ -1)-5$x^{2}$ -5x
2$x^{2}$ +3$x^{2}$ -3-5$x^{2}$ -5x
-5x-3
b)(8-5x)(x+2)+4(x-2)(x+1)+2(X-2)(X+2)+10
(8-5x).(x+2)-4(x+2)(x+1)+2(x-2)(x+2)+10
(x+2)(8-5x-4+x+1+2+x-2)+10
(x-2)(5-3x)+10
( 5x-3$x^{2}$ -10+6x)+10
11x-3$x^{2}$ -10+10
11x-3$x^{2}$
c)4(x-1)(x+5)-(x+2)(x+5)
(x+5)(4x-4-x-2)
(x+5)(3x-2)
3$x^{2}$ -2x +15x -10
(3x+10)(x+1)
Bài 2 :
a) (x+2)(x+3)-(x-2)(x+5)=0
(x+2)(x+3-x-5)=0
(x+2)-2=0
-2x-4=0
-2x=4
x=-2
b)(2x+3)(x-4)-(x-5)(x-2)=(3x-5)(x-4)
(2x+3)(x-4)-(x-5)(x-2)- (3x-5)(x-4)=0
(x-4)(2x+3-3x+5)-(x-5)(x-2)=0
(x-4)(-x+8)-($x^{2}$ -2x-5x+10)=0
(-$x^{2}$ +8x+4x-32)-($x^{2}$ -2x-5x+10)=0
(-$x^{2}$ +12x -32)-($x^{2}$ -7x+10)=0
-$x^{2}$ +12x-32-$x^{2}$ +7x-10=0
-2$x^{2}$ +19x-42=0
-2$x^{2}$+21x-2x-42=0
2x(x-2)+21(x-2)=0
(2x+21)+(x-2)=0
TH1:2x+21=0 TH2: x-2=0
2x=21 x=2
x=10,5
c) (8-5x)(x+2)+4(x-2)(x+1)+2(x-2)(x+2)=0
(8-5x)(x+2)+(X-2)(4x+4+2x+4)=0
(8-5x)(x+2)+(x-2)(6x+8)=0
(8x+16-5$x^{2}$ -10x)+(6$x^{2}$ +8x-12x-16)=0
-2x+16-5$x^{2}$ +6$x^{2}$ +8x-28=0
$x^{2}$ +6x-12=0
