Tính M = a^2(a-1)

To find \( M = a^2(a - 1) \) given the expression

\[
3a - 1 = \frac{3\sqrt{621 - 25}}{2} - \frac{3\sqrt{621 + 25}}{2},
\]

we can start by simplifying the right-hand side.

First, calculate \( \sqrt{621 - 25} \) and \( \sqrt{621 + 25} \):

1. \( \sqrt{621 - 25} = \sqrt{596} \)
2. \( \sqrt{621 + 25} = \sqrt{646} \)

Now substitute these values back into the expression:

\[
3a - 1 = \frac{3\sqrt{596}}{2} - \frac{3\sqrt{646}}{2}
\]

Combine the terms:

\[
3a - 1 = \frac{3}{2}(\sqrt{596} - \sqrt{646})
\]

Now, solve for \( a \):

\[
3a = 1 + \frac{3}{2}(\sqrt{596} - \sqrt{646})
\]
\[
a = \frac{1}{3} + \frac{1}{2}(\sqrt{596} - \sqrt{646})
\]

Now, substitute \( a \) into \( M \):

\[
M = a^2(a - 1)
\]

You can find \( a^2 \) and \( a - 1 \) separately. For the exact numerical solution, substitute the values found for \( a \) into the formula for \( M \) and simplify.