Triangle abc is an obtuse isosceles triangle. angle a measures 20°. what is the number of degrees in the measure of the largest interior angle of tiangle abc

The largest angle must be the single angle, so there are two angles that are 20 degrees. 20 + 20 is 40, and because the sum of all angles in a triangle is 180 degrees, you must subtract 180 - 40, and you get 140 degrees as the largest angle. Hope this helps!