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Supplement Partial Derivatives. 1-D Derivatives (Review). Given f ( x ) . f' ( x ) = d f /d x = Rate of change of f at point x w.r.t. x. f ( x + h ) – f ( x ). h. x. x+h. 1 st -order Partial Derivatives. For a function with 2 variables, f ( x , y ).
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1-D Derivatives (Review) Given f(x). f'(x) = df/dx = Rate of change of f at point x w.r.t. x f(x + h) – f(x) h x x+h
1st-order Partial Derivatives For a function with 2 variables, f(x, y)
Evaluating Partial Derivatives To find fx, we differentiate f w.r.t. x and treat all other variables as constants. Example 1: f(x, y) = x3y2 = (y2)x3 To evaluate fx, y2is to be treated as a constant term. Thus fx = (y2)(3x2) = 3x2y2 Example 2: f(x, y, z) = 10xyz + sin(y)exz3 = (10yz)x + (sin(y)z3)ex To evaluate fx, (10yz) and (sin(y)z3) are to be treated as constant terms. Thus fx = 10yz + (sin(y)z3)ex
Exercise 1) f(x, y) = xexy • fx = • fy = 2) f(x, y, z) = sin (xy) • fx = • fy = • fz =
Exercise f(x, y) = x3 + x2 y – 3xy2 + y3 • fx = • fy = • fxy = • fyx =