For a differential equation

𝑀(𝑥,𝑦)𝑑𝑥+𝑁(𝑥,𝑦)𝑑𝑦=0

we will say it’s exact if and only if

𝜕𝑀𝑑𝑦=𝜕𝑁𝑑𝑥