Understanding the Chain Rule and U-Substitution in Calculus
This lesson focuses on using the chain rule to find derivatives of complex functions, a key concept in calculus. Through various examples, including polynomials and trigonometric functions, learners will understand how to apply the chain rule effectively to calculate derivatives. The session provides a detailed look at both the mathematical process and the underlying principles, reinforcing the relationship between functions and their derivatives. Homework exercises are included to practice the concepts learned.
Understanding the Chain Rule and U-Substitution in Calculus
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Presentation Transcript
Lesson 3-5 Chain RuleorU-Substitutions
Objectives • Use the chain rule to find derivatives of complex functions
Vocabulary • none new
Example 1 Find the derivatives of the following: • g(t) = (5t³ - t + 9)4 • y = (e4x²) (cos 6x) g’(t) = 4 (5t³ - t + 9)³ (15t² - 1) y’(x) = (e4x²) (-sin 6x) (6) + (8x) (e4x²) (cos 6x) = -6 e4x² sin 6x + (8x) (e4x²) (cos 6x)
Example 2 Find the derivatives of the following: d(t) = 360 + 103t – 16t²d’(t³ - 2t² + 1) f(x) = (tan x²) (sin 4x³) d’(t) = 103 – 32t d’(t³ - 2t² + 1) = 103 – 32(t³ - 2t² + 1) = -32t³ + 64t² + 71 f’(x) = tan x² (cos 4x³) (12x²) + (sec² x²) (2x) sin 4x³
Example 3 Find the derivatives of the following: y = 62x-1 f(x) = (tan 2x)³ (3x³ - 4x² + 7x - 9) y’(x) = (ln 6) 62x-1 (2) = (2ln 6) 62x-1 f’(x) = 3(tan 2x)² (2) (3x³ - 4x² + 7x - 9) + (tan 2x)³ (9x² - 8x +7)
Example 4 Assume that f(x) and g(x) are differentiable functions about which we know information about a few discrete data points. The information we know is summarized in the table below: If p(x) = xf(x), find p’(2) If q(x) = 3f(x)g(x), find q’(-2) p’(x) = d(xf(x))/dx = (1) f(x) + f’(x) x p’(2) = (-1) + (5) (2) = -1 + 10 = 9 q’(x) = d(3f(x)g(x))/dx = 3[g’(x) f(x) + f’(x) g(x)] q’(-2) = 3[(6)(4) + (-1)(5)] = 3[24 – 5] = 57
Example 4 cont If r(x) = f(x) / (5g(x)) find r’(0) If s(x) = f(g(x)), find s’(1) r’(x) = d(f(x)/(5g(x)))/dx = (1/5) [g(x) f’(x) - f(x) g’(x)] / g(x)² r’(0) = (1/5)[(8)(-3) - (-6) (-5)] / (8)² = (1/5) [-24 -30] /64 = -54/320 = -0.16875 s’(x) = d(f(g(x)))/dx = f’(x) • g’(x) [chain rule!] s’(1) = (6) (3) = 18
Example 4 cont If t(x) = (2 – f(x)) / g(x) and t’(2) = 4, find g’(2) t’(x) = d((2-f(x)) / g(x))/dx = [g(x) (-f’(x)) – (2-f(x)) g’(x)] / g(x)² t’(2) = 4 = [(1)(-5) - (2-(-1)) (x)] / (1)² = (1/5) [-24 -30] /64 = -54/320 = -0.16875
Summary & Homework • Summary: • Chain rule allows derivatives of more complex functions • Chain rule is also known as u-substitution • Homework: • pg 224 - 227: 3, 4, 7, 8, 11, 14, 15, 22, 29, 32, 43, 67