Use the square root property to solve (y-1)^2+4=0

(y-1)^2 + 4 = 0

(y-1)^2 = -4

take the squareroot of both sides to undo squaring

√(y-1)^2 = +/- √-4

y - 1 = +/- (√4 x √-1)

y = 1 +/- 2i

(y - 1)² = 4 i ²
y - 1 = ± 2i
y = 1 ± 2i