a.\(6x^2-3xy\)

=\(3x\left(2x-y\right)\)

b.\(x^3-16x\)

=\(x\left(x^2-16\right)\)

=\(x\left(x^2-4^2\right)\)

=\(=x\left(x+4\right)\left(x-4\right)\)

a.
A=\(\dfrac{1}{x+4}\)+\(\dfrac{x}{x-4}\)+\(\dfrac{24-x^2}{x^2-16}\)

A=\(\dfrac{1}{x+4}\)+\(\dfrac{x}{x-4}\)+\(\dfrac{24-x^2}{x^2-4^2}\)

A=\(\dfrac{1}{x+4}\)+\(\dfrac{x}{x-4}\)+\(\dfrac{24-x^2}{\left(x+4\right)\left(x-4\right)}\)
MTC:(x + 4)(x - 4)
b.

A=\(\dfrac{1\left(x-4\right)}{\left(x+4\right)\left(x-4\right)}\)+\(\dfrac{x\left(x+4\right)}{\left(x+4\right)\left(x-4\right)}\)+\(\dfrac{24-x^2}{\left(x+4\right)\left(x-4\right)}\)

A=\(\dfrac{x-4+x^2+4x+24-x^2}{\left(x+4\right)\left(x-4\right)}\)

A=\(\dfrac{5x+20}{\left(x+4\right)\left(x-4\right)}\)

A=\(\dfrac{5\left(x+4\right)}{\left(x+4\right)\left(x-4\right)}\)    A=\(\dfrac{5}{\left(x-4\right)}\)

c.

giá trị của biểu thứ A=\(\dfrac{1}{x+4}\)+\(\dfrac{x}{x-4}\)+\(\dfrac{24-x^2}{x^2-16}\) khi x=10

A=​\(\dfrac{1}{10+4}\)+\(\dfrac{10}{10-4}\)+\(\dfrac{24-10^2}{10^2-16}\)​

A=​​\(\dfrac{1}{10+4}\)+\(\dfrac{10}{10-4}\)+\(\dfrac{24-10^2}{\left(10+4\right)\left(10-4\right)}\)

A=\(\dfrac{1+10+24-100}{\left(10+4\right)\left(10-4\right)}\)

A=\(\dfrac{-65}{\left(10+4\right)\left(10-4\right)}\)