SUSTITUCION

3ab-2ad/4ac con a= -2, b= 3, c=1, d= 2

= (3)(-2)(3)-(2)(-1)(2) / 4(-2)(-1)
= -(3*2*3)-(-(2*1*2)) / 4*2*1
= -18+4 / 8 = -14 /8= -7 /4