Algebra 2 students are studying radical expressions this week. Sometimes this unit has felt like a sea of disconnected rules and unfamiliar operations that bog students down and hampers their understanding: many situations are “do this” except if you’re supposed to do something else.
This time, we are working through some well-chosen problems in order to illuminate a few general rules that help students make sense of the material.
Name the Notation & Know the Numbers
We begin by identifying the radical sign, index, and radicand (“stuff under the root”) and making clear the various ways we could say the notation in words.

can be read out loud as “root 2”, “radical 2”, or “square root of 2”.
is “cube root of 2” not “3 root 2”.
We review the perfect square numbers up to 152, the perfect cubes and fourth powers up to base 5, and remind ourselves how easy it is to compute powers of 10.1⤵️
Roots of Products & Quotients

This first set is based on the biconditional
and its cousin
In some of the examples, students must find a perfect square factor (or perfect cube factor), then separate the radicals to simplify. In others, we first combine the radicals to divide away a common factor beforehand.

Also notice in #2, that we don’t have to find the perfect cube factor right away (my students sometimes put on their “concentrating face” until they find the needed factor) but instead, build on knowing 120 = 4•30, then factor 30 into 2•15 to get the 8 we want. And I say about #5 that “the kids inside the house can’t play with the kids outside the house” in order to remember that we cannot further simplify
over 5.
Like Terms & Other Operations
Once students grasp simplifying a radical, they turn to operations. Adding and subtracting require like terms, meaning the same index and radicand. Multiplying situations involve the distributive property and noticing when conjugates are helpful.2⤵️

Remind students that conjugates save you time since you don’t need to perform all four partial products of the “double distribution” (also known as FOIL). Beware of situations when you cannot skip steps such as (x + 1)2 which means (x + 1)(x + 1).

I highlight the reminder to write the index in the “hook” of the radical symbol so it isn’t misinterpreted as an exponent. And there’s two ways to think about
•
; either multiply the radicands to get
or use inverse operations — since squaring undoes the square root.
Devious Denominators
Historically, rationalizing the denominator was used because it made computations (by hand) easier. It also makes adding and subtracting like terms possible, and standardizes what an expression should look like in “simplest form”.3⤵️ Even though calculators are readily available, it nevertheless persists as a topic in many high school math classes.
This set teases out what to do with various denominators, whether single terms of square or higher roots, or binomial denominators requiring the conjugate.

I note to students that the reason why this works is that multiplying top and bottom of a fraction by the same thing is multiplying by a value of 1, which changes the form of the fraction, not the value of the fraction.

In the final step of #14, either factor the common factor in the numerator, then divide away; or “distribute the denominator” into separate fractions. This second method avoids mistakes when there isn’t a common factor of all terms.
Variables in the Radicand
When variables appear in the radicand, students are often told to assume that “all variables are positive” so we don’t need to use absolute value when simplifying.4⤵️
Usually it’s no problem for students to simplify the first two of these, but often they say the third one equals x3, because 9 is a perfect square.

We work through the following sequence of calculations5⤵️ to illuminate the issue (and review the exponent law for multiplying same base). What do you notice about “perfect square” variables?

It turns out that a variable is a perfect square when its exponent is EVEN, not when its exponent is a perfect square. Students also might notice that the square root results in an exponent that is half of the original exponent (more on this below).
I confirm this understanding by asking for the square root of x16 , which is x8, before turning back to the square root of x9. We go through all the steps explicitly for this, but I name the middle two steps as “thinking steps” that students might not need to write out once they learn this process.

Then we turn our attention to perfect cube variables. Students notice that exponents that are multiples of 3 will be perfect cubes, and the cube root divides the exponent by 3.
Continuing on, we examine perfect fourth powers, which will be multiples of 4. Taking the fourth root divides the exponent by 4.


When variables appear in the denominators, figure out how many more factors are needed to make the required power, as we did with numerical denominators for higher index roots.
Tap into the “Power” of Fractional Exponents
Understanding how to simplify a radical expression with variables in the radicand paves the way for the powerful idea of fractional exponents to represent roots.
A fractional exponent represents both the power and the index of the root in one place.

Therefore, any root can be represented as a unit fraction:

This supports our observation about how square roots divide the exponent by 2 and cube roots divide the exponent by 3.
Back to square root of of x9, we can think about it this way (and notice how a mixed number comes in to help out!):

And we want students to be flexible about whether to do the power or root first. There are 2 ways to interpret the fractional exponent.

If you don’t have a calculator, what would you do if asked for 64 to the 3/2 power? Do you want to figure out 643 first or the square root of 64?
Speaking of calculators, the fractional powers are often easier to enter than the roots themselves. Use the ^ exponentiation carat and the stacked fraction symbol. On the TI-84 family, square roots have their own button, and any-index roots are found in the Math Menu or the Alpha-Window shortcut menu.6⤵️

Question 21 uses a fractional exponent instead of a radical symbol. #22 utilizes the exponent law of multiplying exponents when raising a power to another power. In #23, we add exponents when multiplying like bases, and eventually rewrite the answer in radical form.

Many of my students feel that the fractional exponents are easier to handle than roots, because they use those common exponent laws. The remaining two problems are much more detailed. Notice that there are a few different ways to think about the steps, and both ways lead to correct results.

Wrapping Up
The Radical Expressions unit isn’t so scary when we focus on a few important rules and tap into the power of fractional exponents. Taking the time to annotate our work can help students see the thinking behind the steps of the procedure.
Notes & Resources:
All of the examples in this post are available here: Radical Expressions Practice Sheet.
Note that in British English and maths curriculum, radicals are known as “surds”. More on this from the amazing Ben Orlin in US vs. UK: Mathematical Terminology.
1 Divisibility rules for 2, 3, 4, 5, and 9 are worth reviewing. Check out my post Leap Years & License Plates from 2016. ⤴️.
1 continued Also, Steve Walker (@stevemaths.bksy.social) suggests the excellent method of teaching simplifying radicals by prime factorization. I use this when first teaching radicals in 7th/8th grade or Algebra 1, especially if prime factorization is in the curriculum. Jonathan Hall (@studymaths.bsky.social) shows the prime factorization method in this video using the online Prime Factor Tiles manipulative. My Algebra 2 students are already challenged to figure out any factors of the radicand, so I focus on divisibility rules to help get square factors efficiently.
2 More about conjugates and why they are so amazing in my post Powerful Pairs. ⤴️
3 See Why Do We Rationalize the Denominator by Brett Berry. And John Chase (@mrchasemath) also has thoughts in his Rationalization Rant from 2012. And of course “simplest form” is mathematically ambiguous, so I try give my students directions that are as clear as possible; for example, I say “results should have no radicals in the denominator” instead of “write in simplest form”.⤴️
4 Technically, sqrt(x2) = |x| because the principle square root is asked for. This can be a point of confusion; when students are solving an equation such as x2 = 9, the solution is ±3, because the inverse operation of square rooting must consider both positive and negative values of the variable. ⤴️
5 If needed, we remind ourselves that x is actually x1, which is one of several “invisible 1’s” that happen in math notation. Can you think of some others? ⤴️
6 See more about the TI-84 family important keystrokes and menu items in the post Keys For Success. ⤴️
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