The formula to calculate the missing angle (C) is:
\[ C = 180 - (A + B) \]
Where:
Let's say the first known angle (A) is 60 degrees and the second known angle (B) is 80 degrees. Using the formula:
\[ C = 180 - (60 + 80) \]
We get:
\[ C = 40 \, \text{degrees} \]
So, the missing angle is 40 degrees.