Ejercicio 1
\[x^2 - x - 12=0\]
\[x = \boxed{\phantom{\rule{2em}{1.2em}}}\]
Ejercicio 2
\[-x^2 - 5x + 14=0\]
\[x = \boxed{\phantom{\rule{2em}{1.2em}}}\]
Ejercicio 3
\[-3x^2 - 3x + 90=0\]
\[x = \boxed{\phantom{\rule{2em}{1.2em}}}\]