Tricky Math Problem!

pythagorean theorem = 18² = x²+(x+3)²
324 = x² + x² + 6x + 9
0 = 2x² + 6x - 315

x = -b ± sqrt(b²-4ac)
-------------------------
2a
x= -6/4+(√(36+4.2.315))/4
= -1.5+(√2556)/4
= -1.5 + 12.64
= 11.14
another x is impossible because of negative value.
another leg is x+3 = 14.14

x^2 + (x+3)^2 = 18^2
2x^2 +6x + 9 = 324
2x^2 +6x - 315 = 0
Solving,
x = (3/2)(-1 + sqrt(71))
x = (3/2)(-1 - sqrt(71)) (discard)

x²+(x+3)²=18²
x²+x²+6x+9=18
2x²+6x-9=0
x=[-6+(36+72)^0.5)]/4
x=1.098 top leg
x+3=4.098 other leg

x^2 + (x + 3)^2 = 18^2

x^2 + x^2 + 6*x + 9 - 324 = 0

2*x^2 + 6*x - 315 = 0

x = 11.13922466

11.13922466^2 + 14.13922466^2 = 324

i dont understand half those words