$x^2-8x-20$ = 0

D = ${\left(-4\right)}^2-\left(-20\right)$ = $16$$+$ $20$ = $36$

x_1,2 = $4$ ± $\sqrt{36}$

x₁ = $4$ - $6$ = -2

x₂ = $4$ + $6$ = 10

L = { $-2$; $10$}

$-56-x$ = $-x^2$ | - ( $-x^2$)

$-56-x+x^2$ = 0

sortieren

$x^2-x-56$ = 0

D = ${\left(-\frac{1}{2}\right)}^2-\left(-56\right)$ = $\frac{1}{4}$$+$ $56$ = $\frac{1}{4}$$+$ $\frac{224}{4}$ = $\frac{225}{4}$

x_1,2 = $\frac{1}{2}$ ± $\sqrt{\frac{225}{4}}$

x₁ = $\frac{1}{2}$ - $\frac{15}{2}$ = $-\frac{14}{2}$ = -7

x₂ = $\frac{1}{2}$ + $\frac{15}{2}$ = $\frac{16}{2}$ = 8

L = { $-7$; $8$}