B)2x2 - 20 = 6x fórmula general?

<img src="https://tex.z-dn.net/?f=2x%5E2-20%3D6x" />

Restamos 6x de cada lado :

<img src="https://tex.z-dn.net/?f=2x%5E2-20-6x%3D6x-6x" />

Simplificamos :

<img src="https://tex.z-dn.net/?f=2x%5E2-20-6x%3D0" />

<img src="https://tex.z-dn.net/?f=a%3D2%2C%5C%3Ab%3D-6%2C%5C%3Ac%3D-20" />

Primera X :

<img src="https://tex.z-dn.net/?f=%5Cfrac%7B-%5Cleft%28-6%5Cright%29%2B%5Csqrt%7B%5Cleft%28-6%5Cright%29%5E2-4%5Ccdot%20%5C%3A2%5Cleft%28-20%5Cright%29%7D%7D%7B2%5Ccdot%20%5C%3A2%7D" />

Aplicando la regla - ( - a) = a y multiplicando los números 2x2 = 4 :

<img src="https://tex.z-dn.net/?f=%5Cfrac%7B6%2B%5Csqrt%7B%5Cleft%28-6%5Cright%29%5E2-%5Cleft%28-20%5Cright%29%5Ccdot%20%5C%3A2%5Ccdot%20%5C%3A4%7D%7D%7B4%7D" />

Ahora la raíz :

<img src="https://tex.z-dn.net/?f=6%2B%5Csqrt%7B%5Cleft%28-6%5Cright%29%5E2-4%5Ccdot%20%5C%3A2%5Cleft%28-20%5Cright%29%7D%3D6%2B%5Csqrt%7B36-%5Cleft%28-20%5Cright%29%5Ccdot%20%5C%3A8%7D" />

<img src="https://tex.z-dn.net/?f=%5Csqrt%7B36-8%5Cleft%28-20%5Cright%29%7D%3D%5Csqrt%7B36%2B8%5Ccdot%20%5C%3A20%7D%3D%5Csqrt%7B36%2B160%7D%3D%5Csqrt%7B196%7D%3D%5Csqrt%7B14%5E2%7D%3D14" />

Quedaria :

<img src="https://tex.z-dn.net/?f=%3D%5Cfrac%7B6%2B14%7D%7B4%7D%3D%5Cfrac%7B20%7D%7B4%7D%3D5" />

Segunda X :

<img src="https://tex.z-dn.net/?f=%5Cfrac%7B-%5Cleft%28-6%5Cright%29-%5Csqrt%7B%5Cleft%28-6%5Cright%29%5E2-4%5Ccdot%20%5C%3A2%5Cleft%28-20%5Cright%29%7D%7D%7B2%5Ccdot%20%5C%3A2%7D" />

Aplicando la regla - ( - a) = a y multiplicando los números 2x2 = 4 :

[img = 10]

Ahora la raíz :

[img = 11]

[img = 12]

Quedaria :

[img = 13]

Las soluciones al ejercicio serían : [img = 14].