Gilbert Strang, Calculus, 3rd edition (Wellesley-Cambridge Press; MIT OpenCourseWare RES.18-001) §13.4 Directional Derivatives and Gradients, #50 · Multivariable Calculus · Gradient & optimization

Define the derivative of … in the direction … at the point…

Define the derivative of $f (x, y)$ in the direction $u = (u_{1}, u_{2})$ at the point $P = (x_{0}, y_{0})$ . What is $Δ f$ (approximately)? What is $D_{u} f$ (exactly)?

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Gilbert Strang, Calculus, 3rd edition (Wellesley-Cambridge Press; MIT OpenCourseWare RES.18-001) · §13.4 Directional Derivatives and Gradients, #50

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