Partial derivatives are used while we want to investigate the effect of one independent variable on dependent variable. For illustration, the revenues of a farmer may depend on two variables that is; the amount of fertilizer applied and as well the type of the natural soil.
Assume ∏= 30x2y + y2 + 50x + 60y
Whereas ∏ = annual revenue in £ '000'
x = type of soil
y = amount of fertilizer applied