Răspuns:
(4-n)×(5-n) = 12.
Desfacem parantezele:
20-4n-5n+n^2 =12
n^2 - 9n +20 =12 /-12
n^2 -9n +8 =0
delta = 81-32 = 49
n1 = (9+7)/2 = 8
n2 = (9-7)/2 = 1
