Ответы: 1
OKSANA BYKOVEC
2017-11-14 23:08
(х+3)(х-4) = (х+3)(5х+14), х + 3х — 4х — 12 = 5х + 14х + 15х + 42, х — х — 12 = 5х + 29х + 42, х — 5х — х — 29х — 12 — 42 = 0, -4х — 30х — 54 = 0, 2х + 15х + 27 = 0, Д = 15 — 4*2*27 = 225 — 216 = 9, х1 = (-15+3)/2*2 = -12/4 = -3, х2 = (-15-3)/2*2 = -18/4 = -4,5 (или -4 1/2)