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Applying the Power Rule

Abigail Young

Abigail Young

5 min read

Next Topic - Derivative Rules: Constant, Sum, Difference, and Constant Multiple

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Study Guide Overview

This guide covers the Power Rule for finding derivatives in calculus. It explains the rule (f′(x)=n∗x(n−1)f'(x) = n * x^(n-1)f′(x)=n∗x(n−1)), provides a mnemonic ("Drop it Down, Knock it Down"), and emphasizes the derivative of a constant is zero. Practice problems involving various function forms (polynomials, fractions, radicals) are included with solutions and explanations. The guide also highlights common mistakes and provides multiple-choice and free-response practice questions with an answer key. Finally, it offers exam tips focusing on rewriting functions and combining the Power Rule with other calculus rules.

#AP Calculus AB/BC: The Power Rule - Your Ultimate Guide

Hey there, future calculus master! 👋 Let's get you prepped and confident for the AP exam with a deep dive into the Power Rule. This is a major key 🔑, so let's make sure it's locked down tight.

#The Power Rule: Your Derivative Shortcut

#What is it?

The Power Rule is your best friend for finding derivatives of power functions. Instead of dealing with those messy limits, we've got a slick shortcut. If you have a function in the form of f(x)=xnf(x) = x^nf(x)=xn, where 'n' is any constant, here's how to find its derivative:

f′(x)=n⋅x(n−1)f'(x) = n \cdot x^{(n-1)}f′(x)=n⋅x(n−1)

Key Concept

Key Insight: You bring the exponent down, multiply it by the existing coefficient (which is 1 in the basic case), and then reduce the exponent by one. It's like a little dance! 💃

#

Memory Aid

Power Rule Mnemonic: "Drop it Down, Knock it Down"

  • Drop it Down: Bring the exponent down to the front as a coefficient.
  • Knock it Down: Reduce the original exponent by 1. ###
Quick Fact

Quick Fact: Constants Vanish

The derivative of any constant is always zero. This is super important when dealing with polynomials!

#Practice Problems: Let's Get Our Hands Dirty! 🏋️‍♂️

Time to put the Power Rule into action. Remember to rewrite functions if necessary before applying the rule. Let's work through these together:

  1. Given f(x)=x4f(x) = x^4f(x)=x4, find f′(x)f'(x)f′(x).
  2. Given f(x)=1x5f(x) = \frac{1}{x^5}f(x)=x51​, find f′(x)f'(x)f′(x).
  3. Given f(x)=xf(x) = \sqrt{x}f(x)=x​, find f′(x)f'(x)f′(x).
  4. Given f(x)=x6+2x4−10f(x) = x^6 + 2x^4 - 10f(x)=x6+2x4−10, find f′(x)f'(x)f′(x).
Exam Tip

Exam Tip: Always rewrite radicals and fractions as powers before differentiating. This avoids common errors.

#Answers and Explanations: Unlocking the Solutions 👀

  1. Problem: f(x)=x4f(x) = x^4f(x)=x4 Solution: f′(x)=4⋅x(4−1)=4x3f'(x) = 4 \cdot x^{(4-1)} = 4x^3f′(x)=4⋅x(4−1)=4x3

  2. Problem: f(x)=1x5f(x) = \frac{1}{x^5}f(x)=x51​ Solution: First, rewrite f(x)=x−5f(x) = x^{-5}f(x)=x−5. Then, f′(x)=−5⋅x(−5−1)=−5x−6=−5x6f'(x) = -5 \cdot x^{(-5-1)} = -5x^{-6} = \frac{-5}{x^6}f′(x)=−5⋅x(−5−1)=−5x−6=x6−5​

  3. Problem: f(x)=xf(x) = \sqrt{x}f(x)=x​ Solution: First, rewrite f(x)=x12f(x) = x^{\frac{1}{2}}f(x)=x21​. Then, f′(x)=12⋅x12−1=12x−12=12xf'(x) = \frac{1}{2} \cdot x^{\frac{1}{2}-1} = \frac{1}{2}x^{\frac{-1}{2}} = \frac{1}{2\sqrt{x}}f′(x)=21​⋅x21​−1=21​x2−1​=2x​1​

  4. Problem: f(x)=x6+2x4−10f(x) = x^6 + 2x^4 - 10f(x)=x6+2x4−10 Solution: f′(x)=6x5+8x3+0=6x5+8x3f'(x) = 6x^5 + 8x^3 + 0 = 6x^5 + 8x^3f′(x)=6x5+8x3+0=6x5+8x3

Common Mistake

Common Mistake: Forgetting to reduce the exponent by one, or incorrectly applying the rule to constants.

#

Practice Question

Practice Questions

#Multiple Choice Questions

  1. If f(x)=3x4−2x2+7f(x) = 3x^4 - 2x^2 + 7f(x)=3x4−2x2+7, then f′(x)f'(x)f′(x) is: (A) 12x3−4x+712x^3 - 4x + 712x3−4x+7 (B) 12x3−4x12x^3 - 4x12x3−4x (C) 7x3−4x7x^3 - 4x7x3−4x (D) 12x4−4x212x^4 - 4x^212x4−4x2

  2. The derivative of g(x)=4x3g(x) = \frac{4}{x^3}g(x)=x34​ is: (A) 12x2\frac{12}{x^2}x212​ (B) −12x4\frac{-12}{x^4}x4−12​ (C) −43x2\frac{-4}{3x^2}3x2−4​ (D) 43x2\frac{4}{3x^2}3x24​

#Free Response Question

Consider the function h(x)=2x3−5x+6h(x) = 2x^3 - 5\sqrt{x} + 6h(x)=2x3−5x​+6.

(a) Rewrite h(x)h(x)h(x) using exponents instead of radicals. (b) Find h′(x)h'(x)h′(x). (c) Determine the slope of the tangent line to the graph of h(x)h(x)h(x) at x=1x = 1x=1.

Answer Key

Multiple Choice

  1. (B)
  2. (B)

Free Response

(a) h(x)=2x3−5x12+6h(x) = 2x^3 - 5x^{\frac{1}{2}} + 6h(x)=2x3−5x21​+6 (1 point) (b) h′(x)=6x2−52x−12h'(x) = 6x^2 - \frac{5}{2}x^{\frac{-1}{2}}h′(x)=6x2−25​x2−1​ (2 points: 1 for each term) (c) h′(1)=6(1)2−52(1)−12=6−52=72h'(1) = 6(1)^2 - \frac{5}{2}(1)^{\frac{-1}{2}} = 6 - \frac{5}{2} = \frac{7}{2}h′(1)=6(1)2−25​(1)2−1​=6−25​=27​ (1 point)

#Final Exam Focus 🎯

  • Master the Basics: The Power Rule is fundamental and appears in almost every derivative problem.
  • Rewriting Functions: Practice rewriting functions with radicals and fractions as powers. It's a crucial step for applying the Power Rule correctly.
  • Combine with Other Rules: The Power Rule is often used with other rules like the product rule, quotient rule, and chain rule. Make sure you understand how they work together.
Exam Tip

Last-Minute Tip: When you're feeling the pressure, take a deep breath, and remember "Drop it Down, Knock it Down." You've got this!

Let's move on to the next exciting topic! You're doing great! 👍

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Previous Topic - Connecting Differentiability and Continuity: Determining When Derivatives Do and Do Not ExistNext Topic - Derivative Rules: Constant, Sum, Difference, and Constant Multiple

Question 1 of 7

What is the derivative of f(x)=x7f(x) = x^7f(x)=x7?

7x67x^67x6

x6x^6x6

7x87x^87x8

6x76x^76x7