Câu 2:
a/ 2ax2 - 18a
=2a(x2 - 9)
=2a(x-3)(x+3)
b/x3 - x + 3x2 -3
=(x3 + 3x2) - (x + 3)
=x2(x+3) - (x+3)
=(x+3)(x2-1)
=(x+3)(x-1)(x+1)
Câu 1.
a)(x-2)(x+4) - (x-1)2
=x2 + 4x - 2x - 8 - x2 - 2x - 1
= -9
b)\(\dfrac{\left(x+3\right)}{x^2-3x}\)+\(\dfrac{3}{x^2+3x}+\dfrac{\left(2x-18\right)}{x^2-9}\)
=\(\dfrac{\left(x+3\right)}{x\left(x-3\right)}+\dfrac{3}{x\left(x+3\right)}+\dfrac{\left(2x-18\right)}{\left(x-3\right)\left(x+3\right)}\)
=\(\dfrac{\left(x+3\right)^2}{x\left(x-3\right)\left(x+3\right)}+\dfrac{3\left(x-3\right)}{x\left(x+3\right)\left(x-3\right)}+\dfrac{\left(2x-18\right)x}{x\left(x-3\right)\left(x+3\right)}\)
=\(\dfrac{\left(x^2+6x+9+3x-9+2x^2-18x\right)}{x\left(x-3\right)\left(x+3\right)}\)
=\(\dfrac{\left(3x^2-9x\right)}{x\left(x-3\right)\left(x+3\right)}\)
=\(\dfrac{3x\left(x-3\right)}{x\left(x-3\right)\left(x+3\right)}\)
=\(\dfrac{3}{x+3}\)
