First, find the interior angle missing:
Then, we know all the interior angles in a triangle add up to 180º. So, we add all the values for the interior angles and we equate them to 180. We solve the equation normally.
After that, we must add the two angles on a straight line on the right-hand side and equate them to 180.
We compare the equations:
We simultaneously solve by isolating one of the variables () in one of the equations (
) and substituting into the other (
):
We substitute it back into the first formula, the one in which we isolated the variable ():
We now check our answer using the formula we know about the internal angles of a triangle ():
Now, if , then we are correct!
So, in conclusion, and
.
