Помогите решить плиз Х*Х+Х-72=0

Х*Х+Х-72=0 x^2 + x - 72 = 0 D = b^2-4ac = 1^2 - 4*1*(-72) = 1+288 = 289 VD = V289 = 17             -1+17             16 x1 = ------------- = ------------ = 8                 2                   2               -1-17            -18 x2 = -------------- = ----------- = -9                 2                  2     ответ: х=-9 i х = 8