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a) x2 + 6x + 9 = x2 + 2 . x . 3 + 32 = (x + 3)2
b) 10x – 25 – x2 = -(-10x + 25 +x2) = -(25 – 10x + x2)
= -(52 – 2 . 5 . x – x2) = -(5 – x)2
c) 8x3 - 1/8 = (2x)3 – (1/2)3 = (2x - 1/2)[(2x)2 + 2x . 12 + (1/2)2]
= (2x - 1/2)(4x2 + x + 1/4)
d)1/25x2 – 64y2 = (1/5x)2(1/5x)2- (8y)2 = (1/5x + 8y)(1/5x - 8y)
1, 2x2 - 8xy - 5x + 20y
= (2x2 - 5x) - (8xy - 20y)
= x(2x - 5) - 4y(2x - 5)
= (2x - 5) (x - 4y)
2, x3 - x2y - xy + y2
= (x3 - xy) - (x2y - y2)
= x(x2 - y) - y(x2 - y)
= (x2 - y) (x - y)
3, x2 - 2xy - 4z2 + y2
= (x2 - 2xy + y2) - 4z2
= (x - y)2 - (2z)2
= (x - y - 2z) (x - y + 2z)
4, a3 + a2b - a2c - abc
= (a3 - a2c) + (a2b - abc)
= a2(a - c) + ab(a - c)
= (a - c) (a2 + ab)
5, x3 + y3 + 3x2y + 3xy2 - x - y
= (x3 + 3x2y + 3xy2 + y3) - (x + y)
= (x + y) 3 - (x + y)
= (x + y) [(x + y)2 - 1]
= (x + y) (x + y - 1) (x + y + 1)
Bài 1: 4a2-4ab+b2-9a2b2
=(2a)2-2.2a.b+b2-(3ab)2
=(2a-b)2-(3ab)2
=(2a-b-3ab)(2a-b+3ab)
a/ (4a2-4ab+b2)-9a2b2
= (2a-b)2-(3ab)2
= (2a-b-3ab) (2a-b+3ab)
c, =(5x)^3 + (y^2)^ 3 = (5x+y^2)(25x^2 - 5xy^2 + y^4)
d, = (0,5.(a+1))^3-1^3 = ( 0,5(a+1) - 1 ) ( 0,25(a+1) ^2 +a,5(a+1) + 1)
e,2x( x+ 1 ) + 2(x+ 1 ) = 2(x+1)(x+1) = 2(x+1)^2
g, y^2 (x^2 + y) - zx^2 - zy = x^2.y^2 - z.x^2 + y^3 - zy = x^2 (y^2 - z) + y (y^2 -z) = (x^2 +y) (y^2 -z)
h,4.x(x-2y) + 8.y(2y -x) = 4x( x- 2 y ) -8 (x - 2y) = (4x - 8) (x-2y)=4(x-2)(x-2y)
k,=(x+1)(3x(x+1)-5x+7) =(x+1) (3x^2 +3x - 5x + 7)
1) 2x2-8xy-5x+20y
=2x(x-4y)-5(x-4y)
=(2x-5)(x-4y)
2) x3-x2y-xy+y2
=x2(x-y)-y(x-y)
=(x2-y)(x-y)
3) x2-2xy-4z2+y2
=(x-y)2-(2z)2
=(x-y-2z)(x-y+2z)
4) a3+a2b-a2c-abc
=a2(a+b)-ac(a+b)
=(a2-ac)(a+b)
=a(a-c)(a+b)
5) x3+y3+3x2y+3xy2-x-y
=(x+y)(x2-xy+y2)+3xy(x+y)-(x+y)
=(x+y)(x2-xy+y2+3xy-1)
=(x+y)[(x+y)2-1)]
=(x+y)(x+y+1)(x+y-1)
6) x3+x2y-x2z-xyz
=x2(x+y)-xz(x+y)
=(x2-xz)(x+y)
=x(x-z)(x+y)
7) =[x(y+z)2-2xyz]+[y(z+x)2-2xyz]+z(x+y)2
=x(y2+z2)+y(z2+x2)+z(x+y)2
=xy(x+y)+z2(x+y)+z(x+y)2
=(x+y)(xy+z2+zx+zy)
=(x+y)(x+z)(y+z)
8) x3(z-y)+y3(x-z)+z3(y-x)
Tách x-z= -[z-y+y-x]
bạn hỏi từng câu 1 lần thôi cũng đc hỏi 1 lần 17 câu thì thánh nào vô kiên nhẫn trả lời hết đc ^^
a, \(4\left(x-y\right)\left(x+y\right)-5\left(x+y\right)^2=\left(x+y\right)\left[4\left(x-y\right)-5\left(x+y\right)\right]\)
\(=\left(x+y\right)\left(4x-4y-5x-5y\right)=\left(x+y\right)\left(-x-9y\right)=-\left(x+y\right)\left(x+9y\right)\)
b, \(4\left(x+y\right)^2-6\left(x-y\right)\left(x+y\right)=2\left(x+y\right)\left[2\left(x+y\right)-3\left(x-y\right)\right]\)
\(=2\left(x+y\right)\left(2x+2y-3x+3y\right)=2\left(x+y\right)\left(5y-x\right)\)
a, 4(x−y)(x+y)−5(x+y)2
=(x+y)[4(x−y)−5(x+y)]4(x−y)(x+y)−5(x+y)2
=(x+y)[4(x−y)−5(x+y)]
=(x+y)(4x−4y−5x−5y)
=(x+y)(−x−9y)=−(x+y)(x+9y)
=(x+y)(4x−4y−5x−5y)=(x+y)(−x−9y)
=−(x+y)(x+9y)
b, 4(x+y)2−6(x−y)(x+y)
=2(x+y)[2(x+y)−3(x−y)]4(x+y)2−6(x−y)(x+y)
=2(x+y)[2(x+y)−3(x−y)]
=2(x+y)(2x+2y−3x+3y)
=2(x+y)(5y−x)