we have that
x²-8x=39
Group terms that contain the same variable(x²-8x)=39
Complete the square. Remember to balance the equation by adding the same constants to each side
(x²-8x+16)=39+16
Rewrite as perfect squares(x-4)²=55-------> (x-4)²-55=0
(+/-)]x-4]=√55(+)]x-4]=√55--------> x=4+√55
(-)]x-4]=√55-------> x=4-√55
the answer is (x-4)²-55=0