[ Return ]
f = f(x, y) df = f(x + dx, y + dy) - f(x, y) = f(x + dx, y + dy) - f(x, y + dy) + f(x, y + dy)- f(x, y) = f_x.dx + f_y.dy because evaluating the partial derivative at y+dy instead of y doesn't make any difference, right?
Starting to think we need a LaTeX mode.
f = f(x, y) df = f(x + dx, y + dy) - f(x, y) = f(x + dx, y + dy) - f(x, y + dy) + f(x, y + dy)- f(x, y) = (∂f/∂x)dx + (∂f/∂y)dy
dy goes to zero so it makes no difference, yes.
