B = 3/√5+√2 - √(√2-√5)²

To simplify the expression for \( B \):

\[
B = \frac{3}{\sqrt{5} + \sqrt{2}} - \sqrt{(\sqrt{2} - \sqrt{5})^2}
\]

1. **Simplify the square root part**:

\[
\sqrt{(\sqrt{2} - \sqrt{5})^2} = |\sqrt{2} - \sqrt{5}|
\]
Since \(\sqrt{2} < \sqrt{5}\), we have:
\[
|\sqrt{2} - \sqrt{5}| = \sqrt{5} - \sqrt{2}
\]

So we can rewrite \( B \):
\[
B = \frac{3}{\sqrt{5} + \sqrt{2}} - (\sqrt{5} - \sqrt{2})
\]

2. **Combine the two terms**:

For the first term:
\[
B = \frac{3}{\sqrt{5} + \sqrt{2}} - \sqrt{5} + \sqrt{2}
\]

To combine these terms, we may want to get a common denominator. The common denominator is \(\sqrt{5} + \sqrt{2}\).

The first part becomes:
\[
\frac{3}{\sqrt{5} + \sqrt{2}} = \frac{3}{\sqrt{5} + \sqrt{2}}
\]

The second part can be rewritten with the denominator:
\[
-\sqrt{5} + \sqrt{2} = \frac{-\sqrt{5}(\sqrt{5} + \sqrt{2}) + \sqrt{2}(\sqrt{5} + \sqrt{2})}{\sqrt{5} + \sqrt{2}}
\]

This simplifies to:
\[
-\sqrt{5}(\sqrt{5} + \sqrt{2}) + \sqrt{2}(\sqrt{5} + \sqrt{2}) = (-5 + 2) + (-\sqrt{5}\sqrt{2} + \sqrt{5}\sqrt{2}) = -3
\]

So we have:
\[
B = \frac{3 - 3}{\sqrt{5} + \sqrt{2}} = 0
\]

Thus, the final result is:

\[
\boxed{0}
\]