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There can be only one pair of perpendicular lines in an isosceles triangle when it is a right angled isosceles triangle. A non right angled isosceles triangle has no pairs of perpendicular lines.
A triangle can have no parallel lines.
If it is a 45° 45° 90° isosceles right triangle, then there are 2 sides that are perpendicular.
In an equilateral triangle: 3 In an isosceles triangle: 1 In a scalene triangle: 0
None of the sides of any triangle are parallel. However, you can draw an infinite number of parallel lines inside any triangle.