Topic: Nonlinear Equations and Applications
Subtopic: Radical Equations
Overview
Today we will transition from radical expressions to radical equations. We will now be able to solve equations that contain a radical (or two!) for x. The process involves eliminating the radical and solving the resulting equation. You eliminate the radical by isolating it and squaring (or cubing, fourthing, etc.) both sides of the equation.
CAUTION: Be sure to square (or cube, etc.) the entire side of the equation not individual terms. I.e., squaring both sides of √(x)=√(y)+2 does not make x=y+4. Actually it makes x=(√(y)+2)2=(√(y)+2)(√(y)+2) which must then by FOILed.
CAUTION: You must always check your answers when you even-power both sides due to the potential for extraneous solutions. Check by plugging each answer back into the original equation. Then simplify each side to see if they match (and don't power each side to eliminate the radical as that is where the potential error can enter in the first place!).
CAUTION: Recall that an even root can never be equal to a negative number, so something like √(x-5)=-3 is automatically no solution. Don't waste your time trying to solve it.
Besides solving radical equations algebraically you should be able to solve them graphically by electronically graphing each side of the original equation as a separate function and then finding the intersection point (using the INTERSECTION feature of your grapher). If you are using a TI graphing calculator you may want to review my Calculator Guide: Intersection Points for detailed steps.
Objectives
By the end of this topic you should know and be prepared to be tested on:
- 11.1.1 Solve radical equations algebraically that contain:
a single radical (any index), or fractional exponents, or two square roots - 11.1.2 Recognize extraneous solutions to radical equations
- 11.1.3 Determine the number of solutions a radical equation will have by graphing the equation
- 11.1.4 Solve a radical equation by graphing electronically
Terminology
Define: radical equation, extraneous solution
Text Notes
Text:
Intro & Inter Algebra for CS 3ed by Blitzer, sect. 10.6
- Practice solving radical equations both algebraically and graphically -- it is important to be able to solve both ways! The "using technology" box on pg 712 discusses solving a radical equation graphically by finding the x-intercept values.
- Pay attention to the bold-faced statement toward the bottom of page 709 regarding the need to check answers. Not doing so may lead to "extraneous solutions" discussed further at the end of example 2.
- pg 711 Pay attention to the caution/"study tip" -- not doing so will lead to a very common procedural error and lots of wrong answers!