12 . решите уравнения: а) 9x^2-7x-2=0 б) х^2+18х-63=0.

A) 9x² - 7x - 2 = 0
D = b² - 4ac = 49 - 4×9×(-2)= 49 + 72 = 121 = 11²
x1 = ( 7 + 11) / 18 = 1
x2 = (  7 - 11) / 18 = - 4/18 = - 2/9

б) x² + 18x - 63 = 0
D = b² - 4ac = 324 - 4×(-63) = 576 = 24²
x1 = ( - 18 + 24) / 2 = 3
x2 = ( - 18 - 24) / 2 = - 21