3х² + 15х + q = 0,
3*(-12)² + 15*(-12) + q = 0,
3*144 - 180 + q = 0,
432 - 180 + q = 0,
q = -252,
3х² + 15х - 252 = 0,
Д = 15² - 4*3*(-252) = 225 + 3024 = 3249,
х2 = (-15 + 57) / 2*3 = 42/6 = 7
3х² + 15х + q = 0,
3*(-12)² + 15*(-12) + q = 0,
3*144 - 180 + q = 0,
432 - 180 + q = 0,
q = -252,
3х² + 15х - 252 = 0,
Д = 15² - 4*3*(-252) = 225 + 3024 = 3249,
х2 = (-15 + 57) / 2*3 = 42/6 = 7