Bài 1:
\(a.x^2-6xy+9y^2-49\\ =\left(x^2-6xy+9y^2\right)-49\\ =\left(x-3y\right)^2-7^2\\ =\left(x-3y-7\right)\left(x-3y+7\right)\\ b.x^2-6x+5\\ =\left(x^2-x\right)+\left(-5x+5\right)\\ =x\left(x-1\right)-5\left(x-1\right)\\ =\left(x-5\right)\left(x-1\right)\)
Bài 1:
a: \(x^2-6xy+9y^2-49\)
\(=\left(x-3y\right)^2-7^2\)
\(=\left(x-3y-7\right)\left(x-3y+7\right)\)
b: \(x^2-6x+5=x^2-x-5x+5\)
=x(x-1)-5(x-1)
=(x-1)(x-5)
Bài 2: \(A=\dfrac{1}{x-2}+\dfrac{x^2-x-2}{x^2-7x+10}-\dfrac{2x-4}{x-5}\)
\(=\dfrac{1}{x-2}+\dfrac{x^2-x-2}{\left(x-2\right)\left(x-5\right)}-\dfrac{2x-4}{x-5}\)
\(=\dfrac{x-5+x^2-x-2-\left(2x-4\right)\left(x-2\right)}{\left(x-5\right)\left(x-2\right)}\)
\(=\dfrac{x^2-7-\left(2x^2-8x+8\right)}{\left(x-5\right)\left(x-2\right)}\)
\(=\dfrac{x^2-7-2x^2+8x-8}{\left(x-5\right)\left(x-2\right)}=\dfrac{-x^2+8x-15}{\left(x-5\right)\left(x-2\right)}\)
\(=\dfrac{-\left(x-5\right)\left(x-3\right)}{\left(x-5\right)\left(x-2\right)}=\dfrac{-\left(x-3\right)}{x-2}\)
