Решите уравнение (х-3)2+9(х-3)+20=0

Пусть x - 3 = t
t^2 + 9t + 20 = 0 
D= 81 - 80 = 1
t1 = ( - 9 + 1)/2 = - 8/2 = - 4;
t2 = ( - 9 -  1)/2 = - 10/2 = - 5;

x - 3 = - 4
x = - 1

x - 3 = - 5
x = - 2