A quadrilateral with all right angles is a rectangle.
The sum of the interior angles of a quadrilateral is 360 degrees. If three of the angles are right angles, that is, of 90 degrees each, the the fourth must be 90 degrees. So you can have a quadrilateral with three right angles but its fourth angle will also be a right angle. So exactly 3 right angles is not possible.
A rhombus is a quadrilateral that has 4 equal sides and no right angles at its vertices but its digonals intersect each other at right angles.
a quadrilateral where each angle is a right angle
Quadrilateral means four sides. Four right angles and four sides is a rectangle and if the sides are equal length it is a square.
A rhombus is a 4 equal sided quadrilateral that has no corner right angles at its vertices but its two diagonals meet each other at right angles.
A rectangle and a square are two types of quadrilaterals having four equal angles, where each of them equals a right angle.
That is called a rectangle.
A rectangle or a square.
a square or a rectangle
It is a square or a rectangle where each interior angle is a right angle of 90 degrees.
From Wikipedia: "...a rectangle is any quadrilateral with four right angles". So there isn't much to prove, that's how the rectangle is defined.