√(5 - x^2) - √(4 - x^2) = 0.5
(5 - x^2) - 2√((5 - x^2)(4 - x^2)) + (4 - x^2) = 0.25
(5 - x^2) + (4 - x^2) - 0.25 = 2√((5 - x^2)(4 - x^2))
8.75 - 2·x^2 = 2√((5 - x^2)(4 - x^2))
4·x^4 - 35·x^2 + 76.5625 = 4(5 - x^2)(4 - x^2)
4·x^4 - 35·x^2 + 76.5625 = 4·x^4 - 36·x^2 + 80
x^2 - 3.4375 = 0
x = -1.854049621 ∨ x = 1.854049621
Das jetzt einsetzen und Lösung kontrollieren.