Find Directional Derivative

The directional derivative is the gradient dotted with a unit direction vector.

Formula: Dᵤf = ∇f · u, where |u| = 1

Keep rates, balances, prices, and time periods on the same basis. An annual rate should not be combined with a monthly period unless the formula accounts for that conversion.

Check the final amount against the starting figure and rate. A large unexpected difference often points to a period or percentage entered in the wrong form.