None but its apex is perpendicular to its base
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If it has 2 equal acute angles and 1 obtuse angle then it is an isosceles triangle.
A polygon need not have ANY perpendicular or parallel lines. For example, consider an equilateral triangle. It can happen that two sides of a polygon, extended if necessary, meet at a point where they form a 90 degree angle. Those two lines are perpendicular. There may be pairs of lines such that, no matter how far you extend them in either direction, they will never meet. Such lines are parallel. A triangle cannot have parallel lines but it can have perpendicular lines. Any polygon of 4 or more sides can have sides that are perpendicular or parallel (or some of each).
false
When a triangle has 2 sides that are equal in length it is isosceles from Latin and Greek words. Isosceles may also be a mathematical geometric shape with at least 2 sides having the same length.
It is true.