Answer: 102°
Explanation:
First and foremost, we should note that an isosceles triangle has two sides that are equal and that the sum of angles in a triangle equals to 180°.
Since we are told that the isosceles triangle has base angles that each measure 39°, the third angle will be:
t + 39° + 39° = 180°
t + 78° = 180°
t = 180° - 78°
t = 102°
The third angle is 102°.