Calculate the value of the two equal angles in a heptagon if the sum of the other five angles is 780 degrees. 2. Find the sum of the interior angles of a decagon. 3. What is a polygon with nine sides

The sum of 5 angles is given as $780^\circ$.
$$
\text{Sum of remaining 2 angles} = \text{Total sum} - \text{Sum of 5 angles}
$$
$$
\text{Sum of remaining 2 angles} = 900^\circ - 780^\circ = 120^\circ
$$

Since the other two angles are equal, divide their sum by 2.
$$
\text{Value of each angle} = \frac{120^\circ}{2} = 60^\circ
$$
The value of each of the other two angles is $\boxed{\text{60}^\circ}$.

Using the formula $(n-2) \times 180^\circ$:
$$
\text{Sum} = (10-2) \times 180^\circ = 8 \times 180^\circ = 1440^\circ
$$
The sum of angles of a decagon equals $\boxed{\text{1440}^\circ}$.