What would you like to understand?

To expand (5,2)·∇u, substitute ∇$u = (u_x, u_y)$ and apply the definition of the Euclidean dot product: multiply corresponding components and add them. This yields $5u_x + 2u_y$.

Conditions: ∇$u = (u_x, u_y)$.; The dot product is defined as the sum of the products of corresponding components.

To expand (5,2)·∇u, substitute ∇$u = (u_x, u_y)$ and apply the definition of the Euclidean dot product: multiply corresponding components and add them. This yields $5u_x + 2u_y$.

Conditions: ∇$u = (u_x, u_y)$.; The dot product is defined as the sum of the products of corresponding components.