an isosceles triangle is a triangle with two twin sides, and therefore two twin angles.
if one angle is 98°, well, we can't have another 98° angle because that makes 98+98 = 196°, and the sum of all interior angles in a triangle cannot be more than 180°.
so the other remaining angles must be the twin smaller angles, namely 180 - 98 = 82, and each twin takes half of that, namely 41°.
Check the picture below.
