silemus.

46Partial derivative in x

Let f(x,y)=x2y+3xy2\displaystyle f(x, y) = x^2 y + 3xy^2. Find ∂f∂x\displaystyle \frac{\partial f}{\partial x} at (1,2)\displaystyle (1, 2).

Treat y as a constant and differentiate in x: ∂f/∂x = 2xy + 3y². Plugging in (1, 2) gives 2(1)(2) + 3(2)² = 4 + 12 = 16.

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