one way is factor
exg
if you wanted to find the square root of 36 you would factor
36=2 times 2 times 3 times 3
then group repeeting numbers then write only one of them
36=(2 times 2) times (3 times 3)
squareroot36=2 times 3=6
so factor 65
65=5 times 13
that doesn't help
next step
find squares close to that numbers
1^2=1
2^2=4
3^2=9
4^2=16
5^2=25
6^2=36
7^2=49
8^2=64
9^2=81
the answer is a little more than 8
the more exact one would be from a calculator (8.0622577482985)
