Verified answer

(x² - 5x)² - 30x(x - 5) - 216 = 0

[x(x - 5)]² - 30[x(x - 5)] - 216 = 0

Сделаем замену :

x(x - 5) = m

m² - 30m - 216 = 0

D = (- 30)² - 4 * (- 216) = 900 + 864 = 1764 = 42²