2.(a² +b²)= (a-b)² 
=>\(2a^2+2b^2=a^2-2ab+b^2\)

=>\(a^2+2ab+b^2=0\)

=>\(\left(a+b\right)^2=0\)

=>a=-b

Vậy a và b là 2 số đối nhau

ĐKXĐ: x khác 0; x khác -2;2;4

A=\(\dfrac{x^3+x^2-6x}{x^3-4x}=\dfrac{x^2+x-6}{x^2-4}\)

\(=\dfrac{x^2-2x+3x-6}{\left(x-2\right)\left(x+2\right)}\)\(=\dfrac{\left(x+3\right)\left(x-2\right)}{\left(x+2\right)\left(x-2\right)}=\dfrac{x+3}{x+2}\)

Với x=98, ta có:
A\(=\dfrac{x+3}{x+2}=\dfrac{98+3}{98+2}=\dfrac{101}{100}\)