In general, when you have a function of more than one variable, you want to be able to differentiate the function with respect to one of the variables whilst keeping all the others constant. That by definition is the partial derivative.
It has many many applications, but it all boils down to finding slopes / rates of change in particular directions.
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In general, when you have a function of more than one variable, you want to be able to differentiate the function with respect to one of the variables whilst keeping all the others constant. That by definition is the partial derivative.
It has many many applications, but it all boils down to finding slopes / rates of change in particular directions.