x² + = 18

Adding 2 on both sides, we get

x² + + 2 = 18 + 2

x² + + 2 × x × = 20

(x + )² = 20

x + = 2

Given that,

x² + = 18

Subtracting 2 from both sides, we get

x² + - 2 × x × = 18 – 2

(x - )² = 16

x - = 4