z2 + 6z – 8 = 0

(ii) z² + 6z – 8 = 0

Sol. z² + 6z – 8 = 0

∴  z2 + 6z = 8 .... (i)

Third term = ( ½ ×  coefficient of z)²

= ( ½ × 6)²

= (3)²

= 9

Adding 9 to both sides of (i), we get,

z² + 6z + 9 = 8 + 9

∴  (z + 3)² = 17

∴ z + 3 = ±√17

∴ z = - 3 ± √17  

∴  z = –3 + √17 or z = –3 – √17