Explain why an isosceles is acute? Please?

an isosceles triangle is not always acute. you can have an acute isosceles triangle but you could also have an obtuse isosceles if one of the angles is greater than 90 degrees. so if one angle is bigger than a right angle then it is an obtuse.

Not necessarily; An isosceles triangle is a triangle with two angles equal. It can be obtuse say if we have angles 1, 1 and 178. see?

An isosceles has 2 equal angles.
They can´t be >90º because the sum would be greater than 180
so they are less than 90º
The third angle can be greater than 90º

actually an isosceles trainalge DOESNT HAVE to be acute..

take this kind of traingle with these angles 140, 20, 20 degrees and they add up to give 180 deg, which means it is still a triangle , BUT one of the angles is greater than 90, thus this triangle is NOT acute BUT "obtuse"

what you are thinking is this kind of triangle with
50 50 80 deg. which is acute

The angles opposite the two equal sides are the same, because they're opposite sides of equal length and formed by sides of equal length, and all 3 angles must sum to 180. If these two equal angles were not acute, then they would be greater than 90 degrees, so the sum of the angles would exceed 180.