Main content

## 8th grade

### Course: 8th grade > Unit 1

Lesson 2: Square roots & cube roots- Intro to square roots
- Square roots of perfect squares
- Square roots
- Intro to cube roots
- Cube roots
- Worked example: Cube root of a negative number
- Equations with square roots & cube roots
- Square root of decimal
- Roots of decimals & fractions
- Equations with square roots: decimals & fractions
- Dimensions of a cube from its volume
- Square and cube challenge
- Square roots review
- Cube roots review

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# Square roots of perfect squares

Learn how to find the square root of perfect squares like 25, 36, and 81.

Let's start by taking a look at an example evaluating the square root of start color #1fab54, 25, end color #1fab54:

**Step 1:**Ask, "What number squared equals start color #1fab54, 25, end color #1fab54?"

**Step 2:**Notice that start color #11accd, 5, end color #11accd squared equals start color #1fab54, 25, end color #1fab54.

**The answer**

Here's a question to make sure you understood:

# Connection to a square

Finding the square root of start color #1fab54, 25, end color #1fab54 is the same as finding the side length of a square with an area of start color #1fab54, 25, end color #1fab54.

A square with an area of start color #1fab54, 25, end color #1fab54 has a side length of start color #11accd, 5, end color #11accd.

# Practice Set 1:

### Reflection question

# Practice Set 2:

# Practice Set 3:

## Want to join the conversation?

- Can an exponent be a negative number?(68 votes)
- You already know that an exponent represents the number of times you have to multiply a number by itself. A negative exponent is equivalent to the inverse of the same number with a positive exponent. There is nothing special about solving a problem that includes negative exponentials.(14 votes)

- is this 8th-grade math?

im in 5th grade:+(38 votes)- That is awesome for you continue to learn ahead(32 votes)

- easy dubs we gettin out of the gulag with this one(46 votes)
- You are quite the absurd person and I honestly love it(17 votes)

- the most fun part of khan academy is definitely reading the comments...(35 votes)
- What happens if try to find the

the square root of an imperfect square(16 votes)- Most probably it will be an irrational number in which case we can only approximate its value.

However, sometimes we can write the radicand as a fraction of two perfect squares.

Example: √5.76 = √(576∕100) = √(144∕25) = √(12²∕5²) = 12∕5 = 2.4(24 votes)

- we getting outta the hood with this now finna get to college after this(24 votes)
- I just noticed something really interesting (I think):

If I can't remember a square of some numbers (7^2 and 8^2 can be a bit tricky for me for some reason) but I remember the square number of the root that comes before it (6 and 36 in the case I'm trying to find 7^2),

I can do 36+6 to make it into 6*7, and then add a 7 to make it into a 7*7.

I tried to play around and find a rule and I think I found the formula:

n^2 + 2n + 1 = ( n + 1 )^2

(where n is the root number of the square that you do know).

if you would visualize the numbers on a grid, the n^2 is the area of the square, while the 2n+1 is the number of the additional units the is added on the side.

It's easier to see it on a times table: When looking at 25, the number diagonally next to it is 36. If you count the 'units' (the other multiplies that are on the same axes that leads toward 36 IE: 3,6,9 up to 36 on both sides) they will be the same as the 2n+1.

I tried to find a formula for a square of a root that isn't immediately follows the root I know. example: 3^2 = 9, 5^2 = ?.

unfortunately I couldn't think on one consistent formula, because there is always a need to add more and (n+1) with more additional 1s the further the number is.

does the formula I found have a name? I'm pretty sure I wasn't the first to think of that lol(12 votes)- You can use the pascal's triangle I suppose

Edit1: here: https://en.wikipedia.org/wiki/Polynomial_expansion

Edit2: Sorry that is not true. That applies to expansions with higher powers, but not between different sqaures.

But maybe you can look at sum of squares where

∑x^2 = n(n+1)(2n+1)/6(4 votes)

- my math test is tmr pls pray for me(13 votes)
- same, I have two. let's hope we both survive...(9 votes)

- wow

i never actually thought i would ever understand square roots. but theyre actually kinda easy. (i say that now, of course)(14 votes)- lmao i'm sure it'll get harder for us(2 votes)

- So, a perfect square is basically the answer to an exponent? (ex. 2^2(4), 12^12(144))(10 votes)
- it is an integer with a square root that is also an integer(10 votes)