Square Roots and Cube Roots for Kids: Perfect Squares and Cubes (Grade 8 Math)

Hi, I'm Luna from DoodleBeez. Today we are learning about square roots and cube roots. Finding a root means working backwards. We ask which number was multiplied by itself to make this one.

Three times three is nine, so we say three squared is nine. Nine dots make a perfect square with three on each side. The square root of nine is three, the length of one side.

These numbers are perfect squares: one, four, nine, sixteen, twenty five, thirty six, forty nine, sixty four, eighty one and one hundred. Knowing them helps. The square root of sixty four is eight, because eight times eight is sixty four.

Cubing means using a number three times. Two times two times two is eight, so two cubed is eight. The cube root of eight is two. Four cubed is sixty four, so the cube root of sixty four is four.

Roots help us solve equations. If x squared equals forty nine, x could be seven or negative seven, because both make forty nine when squared. If x cubed equals one hundred twenty five, x is five.

Some roots are not whole numbers. Fifty is between forty nine and sixty four, so the square root of fifty is between seven and eight. It is very close to seven, about seven point one.

Now it's your turn. What is the square root of eighty one, and what is the cube root of twenty seven? Pause and try. The square root of eighty one is nine. The cube root of twenty seven is three.

Great job! Remember, a square root undoes squaring and a cube root undoes cubing. Learn your perfect squares and cubes, and use them to estimate other roots. Practice square and cube roots in Middle School Math at doodlebeez.com. See you next time!