In a first year algebra class, students will encounter problems involving simplifying square roots. But many times the teacher simply doesn't explain the process by which this is accomplished in a manner that students can understand. I will explain a way that will make simplifying square roots easier for students of any ability level.
The first method I use when teaching students how to calculate square
root is to look to see if the number is a perfect square first. I
suggest students memorize the perfect squares from 1 to 25 as follows:
1, 4, 9, 16, 25, 49, 64, 81, 100, 121, 144, 169, 196, 225, 256, 289,
324, 361, 400, 441, 484, 529, 576, 625. So if you are asked to calculate
the square root of 441, you automatically know the answer is 21 or -21,
since a negative number times another negative number yields a positive
For non-perfect squares or larger numbers that you are
unsure of, if the number is a perfect square, I suggest using a factor
tree. For example, suppose you want to simplify a square root of 48. It
is not a perfect square since 6 times 6 equals 36 and 7 times 7 equals
49. No whole number times itself equals 48. So break it down into
factors. I always suggest trying to find a perfect square as one of the
factors and in this case, 16 times 3 equals 48 and 16 is a perfect
square. Remember: Since you are dealing with square root, the factors
are also square root. So the square root of 48 equals the square root of
16 times the square root of 3. Three is a prime number so you cannot
break down 3 any farther using a factor tree. We know that the square
root of 16 is 4, so the answer is 4 times the square root of 3.
Another more difficult example---say we need to find the square root of
2025. With such a large number, most people won't know if this is a
perfect square, so use the factor tree. Know that any number ending in 5
is divisible by 5. So 5 times 405 is 2025. But 405 can be broken down
into factors, using the same rule, therefore 5 times 81 is 405. Now we
have the square root of 5 times the square root of 5 times the square
root of 81. Notice then that the square root of 5 times the square root
of 5 equals the square root of 25. Now this problem becomes simple
because you notice we have two perfect squares here, 25 and 81. The
square root of 25 is 5 and square root of 81 is 9. So the answer is 5
times 9, which is 45 and -45, since -45 times -45 equals 2025. This
problem is actually a perfect square, but if you do not recognize it as
such, you can use the factor tree method I just described.
dealing with the square root of a negative number, imaginary numbers
come into play. The square root of -1 equals an imaginary number denoted
as "i". So in the above problems if we had the square root of -48, you
have square root of -1 times square
root of 3 times square root of 16. The answer is 4i times the square
root of 3, and -4i times square root of 3. If we have the square root of
-2025, the answer is simply 45i and -45i.
Hope my method helps you when trying to figure out the square root of both positive and negative numbers.