D==1+80=81
x1=-1+9/2=8/2=4
x2=-1-9/2=-10/2=-5
\begin{lgathered}x {}^{2} + x - 20 = 0 \\\end{lgathered}
x
2
+x−20=0
D=
b {}^{2} - 4acb
−4ac
=1+80=81
=1+80=81