Balls
A quadrilateral.
A triangle.
Side by side, they would form a rectangle. From part-side touching part-side through to corner to corner, they would form a shape somewhat like a figure of eight. There are other possibilities - eg corner of one touching the side of the other.
If there are no angles, all you have is a 'straight side'. There is a plane and no shape. Maybe you are thinking that straight means standing up straight. You might then be thinking of an upright tube.
Balls
A quadrilateral.
A two-dimensional shape with one curved side and four straight sides can be created, but there is not specific name for such a shape.
A triangle.
Side by side, they would form a rectangle. From part-side touching part-side through to corner to corner, they would form a shape somewhat like a figure of eight. There are other possibilities - eg corner of one touching the side of the other.
A shape that has one straight side and one curved side is called a semicircle. A semicircle is a two-dimensional geometric shape that consists of half of a circle. The straight side is the diameter of the circle, while the curved side is the arc that forms half of the circle's circumference.
If there are no angles, all you have is a 'straight side'. There is a plane and no shape. Maybe you are thinking that straight means standing up straight. You might then be thinking of an upright tube.
Yes, a shape can have three straight sides and one curved side. This type of shape is known as a triangle with one curved side, which is also called a curved triangle or a curved-sided triangle. The curved side can be a segment of a circle or any other curved shape, while the other three sides are straight lines.
A shape with at least one side that is not straight, a shape where a pair of straight lines cross one another (like an angular figure of 8).
Extend any straight side of a shape. The angle made by that side with the adjacent side of the shape is an exterior angle. Its value is 180 degrees less the interior angle.
There is no specific name for such a shape.
A scalene triangle.