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.
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.
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.
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.
There is no specific name for such a shape.
If you are referring to a shape, then a semi-circle would be the most likely shape that contains one straight side and one curved. Take a look at a protractor, it's a semi-circle.
A scalene triangle.