Desarrolla (2r - 3s) ^ 3?

Hola.

<img src="https://tex.z-dn.net/?f=%282r-3s%29%5E3" />

Es un binomio al cubo, usaremos está formula :

<img src="https://tex.z-dn.net/?f=%5Cleft%28a-b%5Cright%29%5E3%3Da%5E3-3a%5E2b%2B3ab%5E2-b%5E3" />

Reemplazando :

<img src="https://tex.z-dn.net/?f=%5Cleft%282r%5Cright%29%5E3-3%5Cleft%282r%5Cright%29%5E2%5Ccdot%20%5C%3A3s%2B3%5Ccdot%20%5C%3A2r%5Cleft%283s%5Cright%29%5E2-%5Cleft%283s%5Cright%29%5E3" />

Resolvemos y nos queda :

<img src="https://tex.z-dn.net/?f=%3D%208r%5E3-36r%5E2s%2B54rs%5E2-27s%5E3" />

¡Espero haberte ayudado, saludos!