/ 2 \ log(2/5) log\2/5, x + x - 4/ <= -------- log(x)
log(2/5, x^2 + x - 4) <= log(2/5)/log(x)
/ ____ \ | 1 \/ 21 | And|x <= 2, - - + ------ < x| \ 2 2 /
(x <= 2)∧(-1/2 + sqrt(21)/2 < x)
____ 1 \/ 21 (- - + ------, 2] 2 2
x in Interval.Lopen(-1/2 + sqrt(21)/2, 2)