If the question is about a plane shape with exactly 3 right angles it could be an irregular polygon of 5 or more sides. If the shape can have more than 3 right angles then a square or rectangle are also possible.
Finally, in 3 or more dimensions, a polyhedron with any number of faces can have 3 or more right angles.
pentagon
No because a parallelogram in the shape of a rectangle has 4 right angles
You can make a four sided shape with 3 right angles, but it must have another right angle, too. So technically, yes.
The simplest shape that can have 2 right angles is a rectangle or a square. You can make an unlimited number of more complex shapes, though. A house shape is a pentagon with 2 right angles--you could even make it with 3 right angles.
you cannot make a regular shape which has 3 right angles only, you will always end up with 4 right angles
A seven sided shape is a heptagon.
pentagon
No because a parallelogram in the shape of a rectangle has 4 right angles
You can make a four sided shape with 3 right angles, but it must have another right angle, too. So technically, yes.
The simplest shape that can have 2 right angles is a rectangle or a square. You can make an unlimited number of more complex shapes, though. A house shape is a pentagon with 2 right angles--you could even make it with 3 right angles.
a Pentagon is five sided and CAN have 3 right angles.
you cannot make a regular shape which has 3 right angles only, you will always end up with 4 right angles
A irregular hexagon
A heptagon.
a triangle a triangle
irregular hexagon?
No. The sum of the angles in any 4-sided shape must all ways add up to 360 degrees. So if 3 of the angles in such a shape are right angles the 4th must be as well, which would make the shape a rectangle.