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Section 2.4: The Chain Rule Goals for this Section: Find the derivative of a composite function using the Chain Rule. Find the derivative of a function using the General Power Rule. Simplify the derivative of a function using algebra. Find the derivative of a trigonometric functions using the Chain Rule. 1 Section 2.4: The Chain Rule Theorem 2.10: The Chain Rule If y = f (u) is a differentiable function of u and u = g (x) is a differentiable function of x, then y = f (g (x)) is a differentiable function of x and dy dx = dy du • du dx or, equivalently, d [ f (g (x)) ] = f ' (g (x))•g ' (x) dx d dx f (u) = f ' (u)•u' 2 Section 2.4: The Chain Rule Example: Find the derivative of the function. f (x) = (2x - 5)3 3 Section 2.4: The Chain Rule Example: Find the derivative of the function. f (x) = 3 - 2x 4 Section 2.4: The Chain Rule Example: Find the derivative of the function. f (x) = x ( 3x - 9 )3 5 Section 2.4: The Chain Rule Example: Find the derivative of the function. f (x) = ( 3x - 1 x2 + 3 ( 2 6 Section 2.4: The Chain Rule Theorem 2.11: The General Power Rule If y = [ u (x) ]n , where u is a differentiable function at x and n is a rational number, then dy dx = n[ u (x) ]n-1 du dx or, equivalently, d n] = [ u dx n • un-1 u' 7 Section 2.4: The Chain Rule Trigonometric Functions and the Chain Rule: d dx [ sin u ] (cos u) • u' d dx [ cos u ] = -(sin u) • u' d dx [ tan u ] = (sec2 u) • u' d dx [ cot u ] = -(csc2 u) d dx [ sec u ] = (sec u • tan u ) d dx [ csc u ] = -(csc u • cot u ) = • u' • u' • u' 8 Section 2.4: The Chain Rule Example: Find the derivative of the function. f (x) = sin 2x 9 Section 2.4: The Chain Rule Example: Find the derivative of the function. f (x) = cos x2 10 Section 2.4: The Chain Rule Example: Find the derivative of the function. f (x) = (cos x)2 11 Section 2.4: The Chain Rule Example: Find the derivative of the function. f (x) = sin3 4x 12 Section 2.4: The Chain Rule Example: Evaluate the derivative of the function at the given point. Function f (x) = 5 Point 3x3 + 4x (2,2) 13 Section 2.4: The Chain Rule Example: Find an equation of the tangent line to the graph of f at the given point. Function f (x) = ⅓x Point x2 + 5 (2,2) 14 15