Respuesta :

x - 12√x + 36 = 0
(√x)²  - 2*6√x + 6² = 0 

 We have a perfect square here. (a-b)² =a² - 2ab + b²,
where a= √x and b = 6, 
so for our equation we can write

(√x)²  - 2*6√x + 6² = (√x-6)²

 (√x-6)² = 0
 √x-6 = 0
√x = 6
(√x)² = 6²
x = 6²=36

Check:
x - 12√x + 36 = 0
36 - 12√36+ 36 = 0
36 -12*6 +36=0
72 - 72 = 0 
0=0 True

Answer is B. 6²

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