1. (x-4)^2-28 = 8
(x-4)^2 = 36, we square both sides and get;
x-4 = 6, x = 10
and
x-4 = -6, x = -2
2. The mistake was in step 5.
x² - 6x – 7 = 0; x² - 6x = 7; x² - 6x + 9 = 7 + 9; (x – 3)² = 16
x – 3 = 4; x = 7
x – 3 = -4; x = -1
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Hope this helps!