The expression given in the image is:

D = \sqrt{14 - 2\sqrt{6 - 2\sqrt{6 - 2\sqrt{6 - 2\sqrt{6 - 2\sqrt{6}}}}}}}

Let's simplify it step by step.

Step 1: Simplify the innermost expression

First, consider the innermost expression:

$\sqrt{6}$

Since it's just $\sqrt{6}$, we'll move to the next level:

Step 2: Substitute the innermost expression back

Now substitute back:

$\sqrt{6 - 2\sqrt{6}}$

This expression is already in its simplest form because it involves square roots and is a part of a nested expression.

Step 3: Continue simplification to the outer expressions

The expression then becomes:

$\sqrt{6 - 2\sqrt{6 - 2\sqrt{6}}}$

Continuing similarly, but as we notice that the expressions form a recursive pattern. The structure implies that as the pattern continues, it stabilizes or approaches a fixed value.

Step 4: Solve using recursive patterns

For many similar nested radicals, the pattern often simplifies to a specific integer value, assuming the expressions inside are derived from perfect squares. This results in the whole nested radical simplifying