Réponse :
Bonjour,
[tex]400 + x^2 = (20 + 0,6x)^2\\\\\Leftrightarrow 400 + x^2 = 400 + 24x + 0,36x^2\\\\\Leftrightarrow x^2 - 0,36x^2 + 24x + 400 - 400 = 0\\\\\Leftrightarrow 0,64x^2 + 24x = 0\\\\\Leftrightarrow x(0,64x + 24) = 0[/tex]
Or A × B = 0 ⇔ A = 0 ou B = 0
[tex]x = 0\\\\ou\\\\0,64x - 24 = 0\\\\\Leftrightarrow 0,64x = 24\\\\\Leftrightarrow x = \dfrac{24}{0,64}\\\\\Leftrightarrow x = 37,5[/tex]
Donc S = {0 ; 37,5}