Let's do a long division
color(white)(aaaa)12x^4color(white)(aaaa)12x^3color(white)(aaaa)-5x^2color(white)(aaaa)9xcolor(white)(aaaa)3∣x^2-4
color(white)(aaaa)12x^4color(white)(aaaaaaaa)#color(white)(aaaa)-48x^2#color(white)(aaaa)#color(white)(aaaaaa)#∣12x^2+12x+43
color(white)(aaaaaa)0color(white)(aaaaa)12x^3color(white)(aaa)#color(white)(aaaaaaaaaa)9x#color(white)(aaaaaa)
color(white)(aaaaaa)#color(white)(aaaaaa)12x^3#color(white)(aaaa)+43x^2color(white)(aa)-48xcolor(white)(aa)+3
color(white)(aaaaaa)#color(white)(aaaaaa)0#color(white)(aaaaaaa)+43x^2color(white)(aa)+57x-172color(white)(aaaaaa)
color(white)(aaaaaa)#color(white)(aaaaaa)#color(white)(aaaaaaaaaaaa)0color(white)(aa)+57x+175color(white)(aaaaaa)
Therefore,
(12x^4+12x^3-5x^2+9x+3)/(x^2-4)
=12x^2+12x+43+(57x+175)/(x^2-4)