An isosceles triangle must be an acute triangle______ (judge right or wrong)

An isosceles triangle must be an acute triangle______ (judge right or wrong)

Not necessarily. For example, 120 degrees, 30 degrees, 30 degrees are isosceles triangles, but they are obtuse triangles at the same time; 90 degrees, 45 degrees, 45 degrees are isosceles triangles, and they are right triangles at the same time

If an isosceles triangle and its vertex angle is an acute angle, then the triangle must be an acute angle triangle

Correct

An isosceles triangle whose base angle is greater than the vertex angle must be an acute triangle

Yes, if a base angle is B and a top angle is a, then 3b ＞ 2B + a = 180. B ＞ 60 and B ＜ 90