X2(2=square)+18x+81=0?Quadratic Equation

x² + 18x + 81 = 0

Δ = b² - 4ac = 18² - 4.1.81 = 0
So that only one solution
=> x = -b/2a = -18/2 = -9

Or

x² + 18x + 81 = 0
<=> x² + 2.9.x + 9² = 0
<=> (x + 9)² = 0
<=> x + 9 = 0
<=> x = -9