b, x2+4x+3
=x2+x+3x+3
=x(x+1)+3(x+1)
=(x+1)(x+3)
x, 4x2+4x-3
=4x2-2x+6x-3
=2x(2x-1)+3(2x-1)
=(2x-1)(2x-3)
d, x2-x-12
=x2+3x-4x-12
=x(x+3)-4(x+3)
=(x+3)(x-4)
e, x2-5x+6
=x2-2x-3x+6
=x(x-2)-3(x-2)
=(x-2)(x-3)
f, x2-5x-14
=x2+2x-7x-14
=x(x+2)-7(x+2)
=(x+2)(x-7)
g, 4x2-3x-1
=4x2-4x+x-1
=4x(x-1)+(x-1)
=(x-1)(4x+1)
h, 3x2-2x-5
=3x2+3x-5x-5
=3x(x+1)-5(x+1)
=(x+1)(3x-5)
i, 9x2-6x+1
=9x2-3x-3x+1
=3x(3x-1)-(3x-1)
=(3x-1)(3x-1)
=(3x-1)2
\(\text{a) }x^2-6x+8\\ =x^2-2x-4x+8\\ =\left(x^2-2x\right)-\left(4x-8\right)\\ =x\left(x-2\right)-4\left(x-2\right)\\ =\left(x-4\right)\left(x-2\right)\\ \)
\(\text{b) }x^2+4x+3\\ =x^2+x+3x+3\\ =\left(x^2+x\right)+\left(3x+3\right)\\ =x\left(x+1\right)+3\left(x+1\right)\\ =\left(x+3\right)\left(x+1\right)\\ \)
\(\text{c) }4x^2+4x-3\\ 4x^2+6x-2x-3\\ =\left(4x^2+6x\right)-\left(2x+3\right)\\ =2x\left(2x+3\right)-\left(2x+3\right)\\ =\left(2x-1\right)\left(2x+3\right)\\ \)
\(\text{d) }x^2-x-12\\ =x^2-4x+3x-12\\ =\left(x^2-4x\right)+\left(3x-12\right)\\ =x\left(x-4\right)+3\left(x-4\right)\\ =\left(x+3\right)\left(x-4\right)\\ \)
\(\text{Chữa đề: }\\\text{e) }x^2-5x-6\\ =x^2-6x+x-6\\ =\left(x^2+x\right)-\left(6x+6\right)\\ =x\left(x+1\right)-6\left(x+1\right)\\ =\left(x-6\right)\left(x+1\right)\\ \)
\(\text{f) }x^2-5x-14\\ =x^2-7x+2x-14\\ =\left(x^2-7x\right)+\left(2x-14\right)\\ =x\left(x-7\right)+2\left(x-7\right)\\ =\left(x+2\right)\left(x-7\right)\\ \)
\(\text{g) }4x^2-3x-1\\ =4x^2-4x+x-1\\ =\left(4x^2-4x\right)+\left(x-1\right)\\=4x\left(x-1\right)+\left(x-1\right)\\ =\left(4x+1\right)\left(x-1\right)\\ \)
\(\text{h) }3x^2-2x-5\\ =3x^2-5x+3x-5\\ =\left(3x^2+3x\right)-\left(5x+5\right)\\ =3x\left(x+1\right)-5\left(x+1\right)\\ \left(3x-5\right)\left(x+1\right)\\ \)
\(\text{ i) }9x^2-6x+1\\ =\left(3x\right)^2-2\cdot3x\cdot1+1^2\\ =\left(3x-1\right)^2\)
Lần sau đăng từ từ thôi nhé.
