a right triangle is (always sometimes never) an isosceles triangle

Answer 1

Sometimes. Consider a ladder leaning against a wall. While it could be placed so that the distance up the wall from the ground to the ladder is equal to the distance from the wall along the ground to the ladder's other end (thus making an isosceles right triangle), it by no means has to be. If you shift the end of the ladder either up the wall or down it, it still forms a right triangle, but not an isosceles one.