In how many ways can you arrange the books A, B, C, and D on a bookshelf if books A and C must remain neighboring?

Find the area of the regular hexagon if a side is 20 cm.

A3-dimensional figure has a square base and 4 lateral faces that meet at a point. explain the difference between the cross sections when a slice is made perpendicular to the base through the vertex, and when a slice is made perpendicular to the base and not through the vertex

The surface area of the triangular prism is .