If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content

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:
square root of, start color #1fab54, 25, end color #1fab54, end square root, equals, question mark
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.
start color #11accd, 5, end color #11accd, squared, equals, start color #11accd, 5, end color #11accd, times, start color #11accd, 5, end color #11accd, equals, start color #1fab54, 25, end color #1fab54
The answer
square root of, start color #1fab54, 25, end color #1fab54, end square root, equals, start color #11accd, 5, end color #11accd
Here's a question to make sure you understood:
How can we be sure that start color #11accd, 5, end color #11accd is the right answer?
Choose 1 answer:

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:

Problem 1A
  • Current
4, squared, equals
  • Your answer should be
  • an integer, like 6
  • a simplified proper fraction, like 3, slash, 5
  • a simplified improper fraction, like 7, slash, 4
  • a mixed number, like 1, space, 3, slash, 4
  • an exact decimal, like 0, point, 75
  • a multiple of pi, like 12, space, start text, p, i, end text or 2, slash, 3, space, start text, p, i, end text

Reflection question

Which claim shows how square roots work?
Choose 1 answer:

Practice Set 2:

Problem 2A
  • Current
square root of, 1, end square root, equals
  • Your answer should be
  • an integer, like 6
  • a simplified proper fraction, like 3, slash, 5
  • a simplified improper fraction, like 7, slash, 4
  • a mixed number, like 1, space, 3, slash, 4
  • an exact decimal, like 0, point, 75
  • a multiple of pi, like 12, space, start text, p, i, end text or 2, slash, 3, space, start text, p, i, end text

Practice Set 3:

Problem 3A
  • Current
square root of, 121, end square root, equals
  • Your answer should be
  • an integer, like 6
  • a simplified proper fraction, like 3, slash, 5
  • a simplified improper fraction, like 7, slash, 4
  • a mixed number, like 1, space, 3, slash, 4
  • an exact decimal, like 0, point, 75
  • a multiple of pi, like 12, space, start text, p, i, end text or 2, slash, 3, space, start text, p, i, end text

Want to join the conversation?

  • blobby green style avatar for user cyanne.13.edwards
    Can an exponent be a negative number?
    (67 votes)
    Default Khan Academy avatar avatar for user
    • duskpin seedling style avatar for user Joann
      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.
      (13 votes)
  • duskpin tree style avatar for user ELLEN
    is this 8th-grade math?
    im in 5th grade:+
    (37 votes)
    Default Khan Academy avatar avatar for user
  • male robot donald style avatar for user Saaketh Gaddam
    What happens if try to find the
    the square root of an imperfect square
    (16 votes)
    Default Khan Academy avatar avatar for user
  • mr pink red style avatar for user minnieli1223
    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)
    Default Khan Academy avatar avatar for user
  • hopper cool style avatar for user maruandtotoro
    So, a perfect square is basically the answer to an exponent? (ex. 2^2(4), 12^12(144))
    (10 votes)
    Default Khan Academy avatar avatar for user
  • female robot ada style avatar for user aniza white
    How can we use square roots in life?
    (8 votes)
    Default Khan Academy avatar avatar for user
  • blobby green style avatar for user MasonK
    [Hook]
    "Don't worry about a thing
    'Cause every little thing is gonna be alright"
    Singing, "Don't worry about a thing
    'Cause every little thing is gonna be alright!"

    [Chorus]
    Rise up this morning, smiled with the rising sun
    Three little birds pitch by my doorstep
    Singing sweet songs of melodies pure and true
    Saying, "This is my message to you-ou-ou"

    [Hook]
    Singing, "Don't worry about a thing
    'Cause every little thing is gonna be alright"
    Singing, "Don't worry about a thing (Don't worry)
    'Cause every little thing is gonna be alright!"

    [Chorus]
    Rise up this morning, smiled with the rising sun
    Three little birds pitch by my doorstep
    Singing sweet songs of melodies pure and true
    Saying, "This is my message to you-ou-ou"

    [Hook]
    Singing, "Don't worry about a thing (Worry about a thing, oh)
    'Cause every little thing is gonna be alright (Don't worry)
    Singing, "Don't worry about a thing (I won't worry)
    'Cause every little thing is gonna be alright!"
    Singing, "Don't worry about a thing
    'Cause every little thing is gonna be alright (I won't worry)
    Singing, "Don't worry about a thing
    'Cause every little thing is gonna be alright!"
    Singing, "Don't worry about a thing (Don't worry about a thing)
    'Cause every little thing is gonna be alright
    (10 votes)
    Default Khan Academy avatar avatar for user
  • leafers seedling style avatar for user jl974294
    How do you solve square roots that can't be squared easily?
    (8 votes)
    Default Khan Academy avatar avatar for user
  • blobby green style avatar for user AdalineO
    How are you doing?
    (7 votes)
    Default Khan Academy avatar avatar for user
  • primosaur tree style avatar for user osagier430
    can a decimal have a square root
    (6 votes)
    Default Khan Academy avatar avatar for user