Los 4 pasos de la regla son :
a) incremento de las dos variables
b) realizar las operaciones algebraicas y restar la función original
c) hacer el cociente incremental
d) hacer lím cuando <img src="https://tex.z-dn.net/?f=%5CDelta%20x%5Cto%200" />
Te hago la primera :
<img src="https://tex.z-dn.net/?f=y%3Dx%5E2-3x%2B4%5Cto%20%28y%2B%5CDelta%20y%29%3D%28x%2B%5CDelta%20x%29%5E2-3%28x%2B%20%5CDelta%20x%29%2B4" />
<img src="https://tex.z-dn.net/?f=y%2B%5CDelta%20y%3Dx%5E2%2B%5CDelta%20x%5E2%2B2x%5CDelta%20x-3x-3%5CDelta%20x%2B4%5Cto%20" />
<img src="https://tex.z-dn.net/?f=y%2B%5CDelta%20y-y%3Dx%5E2%2B%5CDelta%20x%5E2%2B2x%5CDelta%20x-3x-3%5CDelta%20x%2B4-x%5E2%2B3x-4" />
<img src="https://tex.z-dn.net/?f=%5CDelta%20y%3D%5CDelta%20x%5E2%2B2x%5CDelta%20x-3%5CDelta%20x%5Cto%20%5Cfrac%7B%5CDelta%20y%7D%7B%5CDelta%20x%7D%3D%5Cfrac%7B%5CDelta%20x%5E2%2B2x%5CDelta%20x-3%5CDelta%20x%7D%7B%5CDelta%20x%7D" />
<img src="https://tex.z-dn.net/?f=%5Cfrac%7B%5CDelta%20y%7D%7B%5CDelta%20x%7D%3D%5CDelta%20x%2B2x-3" />
<img src="https://tex.z-dn.net/?f=%20%5Cdisplaystyle%20y%27%3D%5Clim_%7B%5CDelta%20x%20%5Cto%200%7D%20%5Cfrac%7B%5CDelta%20y%7D%7B%5CDelta%20x%7D%3D%5Clim_%7B%5CDelta%20x%20%5Cto%200%7D%20%28%5CDelta%20x%2B2x-3%29%3D2x-3%20" />.