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Digital SAT Math
Course: Digital SAT Math > Unit 12
Lesson 9: Radical, rational, and absolute value equations: advancedRadical, rational, and absolute value equations | Lesson
A guide to radical, rational, and absolute value equations on the digital SAT
What are radical, rational, and absolute value equations?
Radical equations are equations in which variables appear under radical symbols ( ).
is a radical equation.
Rational equations are equations in which variables can be found in the denominators of rational expressions.
is a rational equation.
Both radical and rational equations can have extraneous solutions, algebraic solutions that emerge as we solve the equations that do not satisfy the original equations. In other words, extraneous solutions seem like they're solutions, but they aren't.
Absolute value equations are equations in which variables appear within vertical bars ( ).
is an absolute value equation.
In this lesson, we'll learn to:
- Solve radical and rational equations
- Identify extraneous solutions to radical and rational equations
- Solve absolute value equations
You can learn anything. Let's do this!
How do I solve radical equations?
Intro to square-root equations & extraneous solutions
What do I need to know to solve radical equations?
The process of solving radical equations almost always involves rearranging the radical equations into , then solving the quadratic equations. As such, knowledge of how to manipulate polynomials algebraically and solve a variety of quadratic equations is essential to successfully solving radical equations.
To solve a radical equation:
- Isolate the radical expression to one side of the equation.
- Square both sides the equation.
- Rearrange and solve the resulting equation.
Example: If , what is the value of ?
When it comes to extraneous solutions, the concept that confuses the most students is that of the principal square root. The square root operation gives us only the principal square root, or positive positive square root. For example, , not both and even though . If a solution leads to equating the square root of a number to a negative number, then that solution is extraneous.
To check for extraneous solutions to a radical equation:
- Solve the radical equation as outlined above.
- Substitute the solutions into the original equation. A solution is extraneous if it does not satisfy the original equation.
Example: What is the solution to the equation ?
Try it!
How do I solve rational equations?
Equations with rational expressions
What do I need to know to solve rational equations?
Knowledge of fractions, polynomial operations and factoring, and quadratic equations is essential for successfully solving rational equations.
To solve a rational equation:
- Rewrite the equation until the variable no longer appears in the denominators of rational expressions.
- Rearrange and solve the resulting linear or quadratic equation.
Example: If , what is the value of ?
Most often, the reason a solution to a rational equation is extraneous is because the solution, when substituted into the original equation, results in division by . For example, if one of the solutions to a rational equation is and the original equation contains the denominator , then the solution is extraneous because , and we cannot divide by .
To check for extraneous solutions to a rational equation:
- Solve the rational equation as outlined above.
- Substitute the solution(s) into the original equation. A solution is extraneous if it does not satisfy the original equation.
Example: What value(s) of satisfies the equation ?
Try it!
How do I solve absolute value equations?
Absolute value equation with two solutions
Absolute value equation with no solution
The absolute value of a number is equal to the number's distance from on the number line, which means the absolute value of a nonzero number is always positive. For example:
- The absolute value of
, or , is . - The absolute value of
, or , is also .
Practically, this means every absolute value equation can be split into two linear equations. For example, if :
- The absolute value equation is true if
. - The absolute value equation is also true if
since .
When solving absolute value equations, rewrite the equation as two linear equations, then solve each linear equation. Both solutions are solutions to the absolute value equation.
Example: What are the solutions to the equation ?
Try it!
Your turn!
Things to remember
The radical operator ( ) calculates only the positive square root. If a solution leads to equating the square root of a number to a negative number, then that solution is extraneous.
We cannot divide by . If a solution leads to division by , then that solution is extraneous.
For the absolute value equation , rewrite the equation as the following linear equations and solve them.
Both solutions are solutions to the absolute value equation.
Want to join the conversation?
- Upvote if you think Sal rocks 🤘🏽(207 votes)
- I did 👍 All for Sal, and Sal for all!(10 votes)
- in a few years this comment section will be filled and we will become history(56 votes)
- What date are you guys doing the digital SAT?(2 votes)
- oct 7 2023.....
pray for me(29 votes)- I take it on August 26th :/(19 votes)
- why do they always opt for the harder methods when there are easier and faster methods(10 votes)
- been studying for the SAT i have saturday (3/11/23) ill let you guys know how i did(3 votes)
- he lied....(15 votes)
- This lesson tells us to take only the positive value out of a square root whereas the lesson before this(solving quadratic equations)tells us to take both the positive and the negative value. How do I know when to follow which lesson on the test?(8 votes)
- can someone explain how sqrt(8t) can also be written or simplified to 2*sqrt(2t) ?(4 votes)
- one of the rules of roots is that sqrt(a * b) = sqrt(a) * sqrt(b)
sqrt(8t) = sqrt(4 * 2t) = sqrt(4) * sqrt(2t) = 2sqrt(2t).(3 votes)
- easiest way to get the solutions and correct ones every time is to just plot the initial equations on desmos no?(5 votes)
- absolute value was so hard to understand, all because of this damn explnation(4 votes)