In an isosceles triangle, if a base angle has a measure of 43 degrees, then the vertex angle must have a measure of 80 degrees as well. true or false?

False because the interior angles of any triangle needs to add up to 180°. In an isoceles triangle, the base angles of the triangle are equal so 43° + 43° = 86°. If the vertex angle is 80° then the total is 166°. This doesn't meet 180°, so the vertex angle must be 94° if the base angles are 43°. If the vertex angle must be 80°, then the base angles have to be 50°.