Am i doing this right. someone help me.

What is the missing step in this proof ?

For the following geometric sequence, find the recursive formula. {-80, 20, -5, } i need : ')

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