Prove that in a tetrahedron if two pairs of opposite edges are perpendicular , then the third pair is also perpendicular.

In a tetrahedron, if two pairs of opposite edges are perpendicular to each other, prove that the third pair is also perpendicular and that the sum of the squares on the two opposite edges is same for each pair.

If two pairs of opposite sides are equal in a quadrilateral then it is called …………….

Prove that any two opposite edges in a regular tetrahedron are perpendicular.

Are the edges of postcard perpendicular?

Pair of straight lines perpendicular to each other are represented by

Pair of straight lines perpendicular to each other are represented by

Prove that if both pairs of opposite sides of a quadrilateral are equal, then it is a parallelogram.

The edges of this instrument are perpendicular to each other?

Name two pairs of vertically opposite angles in the figure.