Question

resolva a equação (x-4)²=x²-40

Answer 1

x² - 8x + 16 = x² - 40
cancela x²
- 8x = - 40  - 16 
- 8x = -56
    x = 56/8
    x = 7

Answer 2

$(x-4)^2=x^2-40\to \\\\ x^2-4x-4x+16=x^2-40\to \\\\ \not x^2-8x+16-\not x^2+40=0\to \\\\ -8x+56=0\to \\\\ -8x=-56~(-1)\to \\\\ 8x=56\to \\\\ x= \dfrac{56}{8} \to\\\\ \boxed{x=7}$