# How do you simplify #sqrt15 times sqrt21#?

##### 3 Answers

#### Explanation:

When multiplying 2 square roots they can be combined into one.

Write each number as the product of its prime factors.

=

#### Explanation:

When simplifying roots of natural numbers is is often useful to first express the numbers as the product of prime numbers.

Consider:

Also:

Same thing but with a slight twist in approach

#### Explanation:

Look for common factors. Notice that 3 will divide into both 15 and 21 with no remainder.

Write as:

You can split these in the following way:

But

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