0,2x^-0,4x+1=17,20 je n’y arrive pas...

Bonsoir,

[tex]0,2x^ -0,4x+1=17,20\\\Longrightarrow\ 0.2x^2-0.4x+1=17.2\\\Longrightarrow\ 0.2x^2-0.4x+1-17.2=0\\\Longrightarrow\ 0.2x^2-0.4x-16.2=0\\\Longrightarrow\ 2x^2-4x-162=0\\\Longrightarrow\ x^2-2x-81=0\\ \Delta=2^2+4*81=328=2^3*41\\x=\dfrac{2-2\sqrt{82}}{2} \ ou\ x=\dfrac{2+2\sqrt{82}}{2}\\x=1-\sqrt{82}\ ou\ x=1+\sqrt{82}[/tex]