Which statement describes a convex surface?

Which statement describes a convex surface?

• A. A surface that is curved outward in the middle.
• B. A surface that is curved inward in the middle.
• C. A flat surface.
• D. A surface that is completely spherical.

Answer: (A)

The main idea here is how a surface bends relative to its interior. A convex surface bulges outward, so the middle of the surface sits higher with respect to the interior side. That outward bending is exactly what is described by “curved outward in the middle,” making it the best way to describe a convex surface. In contrast, a surface curved inward in the middle is concave, like the inside of a bowl. A flat surface has no bending at all, so it isn’t described as convex or concave. A completely spherical surface is an example of a convex surface, but the description given—curved outward in the middle—captures the outward bending property that defines convexity.

The main idea here is how a surface bends relative to its interior. A convex surface bulges outward, so the middle of the surface sits higher with respect to the interior side. That outward bending is exactly what is described by “curved outward in the middle,” making it the best way to describe a convex surface.

In contrast, a surface curved inward in the middle is concave, like the inside of a bowl. A flat surface has no bending at all, so it isn’t described as convex or concave. A completely spherical surface is an example of a convex surface, but the description given—curved outward in the middle—captures the outward bending property that defines convexity.