3. what line forms when a plane and a cylinder intersect?

The answer to this depends on the angle at which they intersect. If it intersects the cylinder perpendicular to the axis then a circle is formed. If the plane intersects the cylinder at an angle, it will form an ellipse. This will be true until the plan is parallel with the axis of the cylinder. At that point, the surface will become a rectangle.

You can find the area of a rectangle by multiplying the length and height. so multiply 1/2*7/4(which is the simpler version of 1 3/4) and you get 7/8 as your answer.

The right answer is option d.