Maths problem, how to do b,?

Smile 新年進步。

(a)
1/[x(x+1)] = -4
1 = -4x(x+1) where x(x+1)≠0
-4x² - 4x = 1 where x ≠ 0 and x + 1 ≠ 0
4x² + 4x + 1 = 0  where x ≠ 0 and x ≠ -1
(2x + 1)² = 0
x = -1/2

(b)
Let x = 2^(y+1) - 1.
Then,
1/{[2^(y+1) - 1]2^(y+1)} = -4
1/[x(x+1)] = -4
x = -1/2
2^(y+1) - 1 = -1/2
2^(y+1) = 1/2
2^(y+1) = 2^(-1)
y+1 = -1
y = -2