√21 (√3+ √14)

Let's start by simplifying the expression inside the parentheses:

√3 + √14

Now, we can simplify √14 by breaking it down into factors of a perfect square:

√14 = √(2*7) = √2 * √7

So, now our expression becomes:

√3 + √2 * √7

Now, we can multiply √3 by both terms under the square root:

√3 * √2 = √6

Therefore, our expression becomes:

√6 + √7

Now, we can multiply √21 by the simplified expression:

√21 * (√6 + √7) = √21 * √6 + √21 * √7
= √(21*6) + √(21*7)
= √126 + √147

Therefore, the simplified form of √21 (√3 + √14) is √126 + √147.