Which is not true about an acute isosceles triangle?

a. two sides measure the same b. all angle measures are less than 90 degrees

c. one angle is obtuse d. two angles all measure the same

The answer is C. None of the angles are obtuse. In an isoscoles triangle, two sides are the same length which means two angles are the same and if its acute, then all of the angles are less than 90 degrees

An isosceles triangle has two sides which have the same length, and one side with a different length, so A is true.

It also has two angles which are the same, and one angle which is different, so D is true.

Acute angles are always less than 90°, so B is also true.

C is NOT true because the triangle is an acute isosceles and the other statements are true.

Answer = C