How do you simplify square root 18 – square root 98?

To simplify the expression √18 - √98, we can start by simplifying the square roots individually.

√18 can be simplified as follows:
√18 = √(9 × 2) = √9 × √2 = 3√2

Similarly, √98 can be simplified as follows:
√98 = √(49 × 2) = √49 × √2 = 7√2

Now we can substitute these simplified square roots back into the original expression:

√18 - √98 = 3√2 - 7√2

Since the terms have the same radical (√2), we can combine them:

3√2 - 7√2 = (3 - 7)√2 = -4√2

Therefore, the simplified form of √18 - √98 is -4√2.