Question

найдите нули функции у=$x^{2}$ - 4х-21

Answer 1

$x^{2} - 4x-21 = 0; \ D = 16 + 84 = 100; \ x1= (4 + 10)/2; \ x2= (4 - 10)/2 ; \ x1 =7, x2= -3$