Green Bridge Learning Resource For Substitution To Solve Equations

Overview

Some equations look frightening until you notice a hidden quadratic inside them. By naming a repeated chunk with a new letter, you can turn a quartic, or an equation in powers of \(e^x\), into a plain quadratic you already know how to solve. This change of variable is one of the most elegant tricks in algebra.

In this lesson you will learn to spot a substitution such as \(u=x^2\), solve the resulting quadratic, and then return to the original variable to finish. The classic example is \(x^4-5x^2+4=0\), which becomes \(u^2-5u+4=0\) and unlocks four solutions.

Lesson Evaluation

Congratulations on completing the lesson on Substitution To Solve Equations. Now that youve explored the key concepts and ideas, its time to put your knowledge to the test. This section offers a variety of practice questions designed to reinforce your understanding and help you gauge your grasp of the material.

You will encounter a mix of question types, including multiple-choice questions, short answer questions, and essay questions. Each question is thoughtfully crafted to assess different aspects of your knowledge and critical thinking skills.

Use this evaluation section as an opportunity to reinforce your understanding of the topic and to identify any areas where you may need additional study. Don't be discouraged by any challenges you encounter; instead, view them as opportunities for growth and improvement.

Using u = x^2, the equation x^4 - 5x^2 + 4 = 0 becomes: A. u^2 - 5u + 4 = 0 B. u^2 + 5u + 4 = 0 C. u - 5u + 4 = 0 D. 2u - 5 = 0 Answer: A
How many real solutions has x^4 - 5x^2 + 4 = 0? A. 1 B. 2 C. 3 D. 4 Answer: D
Solve x^4 - 5x^2 + 4 = 0. A. x = 1 or x = 4 B. x = +/-1 or x = +/-2 C. x = +/-1 or x = +/-4 D. x = 2 only Answer: B
For e^{2x} - 3e^x + 2 = 0, the substitution u = e^x gives the values: A. u = 1 or u = 2 B. u = -1 or u = -2 C. u = 0 or u = 3 D. u = 2 only Answer: A
Solve e^{2x} - 3e^x + 2 = 0. A. x = 0 or x = ln 2 B. x = 1 or x = 2 C. x = ln 2 only D. x = -1 or x = -2 Answer: A