Question 1042298
You can do your others using Matrix, Elimination, or Substitution.  This one, you might want to use Substituion.  


Substitute expression for y from one equation into the other equation.


{{{y=x^2-4}}}
{{{3x-6=x^2-4}}}-----the substitution
{{{3x-6-x^2+4=0}}}
{{{-3x+6+x^2-4=0}}}
{{{x^2-3x+6-4=0}}}
{{{x^2-3x+2=0}}}---------USE FACTORIZATION AND ZERO-PRODUCT RULE.