Respuesta :

ghanami

Answer:

two solutions : 9   ; -9

Step-by-step explanation:

x²=81

means : x² - 81 =0   but 81 = 9²

use identity ; a² - b² = (a-b)(a+b)

x² -9² = 0     : (x-9)(x+9)=0

x-9=0 or x+9 = 0

x =9 or x = -9