1) (- infinito;-5) U (4; +infinito)

2) a = 1/6       f(x):1/6 (x-1) (x+2)

3) a = -10       c+ (2;+infinito)      c- (-infinito;0) U (0;2)

h-1(x): [ln (x-6)+3] /2

h (7) = Y = 3/2