$$ 16z^2+8( i+1)z +2(i+\frac 92)=0 $$
$$ 16z^2+2 \cdot 4z \cdot ( i+1) =-2(i+\frac 92) $$
$$ 16z^2+2 \cdot 4z \cdot ( i+1)+( i+1)^2 =-2(i+\frac 92) +( i+1)^2$$
$$ ( 4z +( i+1))^2 =-2(i+\frac 92) +( i+1)^2$$
$$ ( 4z +( i+1))^2 =-2i- 9 +( i^2+2i+1)$$
$$ ( 4z +( i+1))^2 =-2i- 9 +( -1+2i+1)$$
$$ ( 4z +( i+1))^2 =-2i- 9 +2i$$
$$ ( 4z +( i+1))^2 =- 9 $$
$$ 4z +( i+1) =\pm 3i $$