Which expression is equivalent to -1?
a) -
x + y
x - y
b) -
x - y
-x + y
c) -
x - y
-x - y
d) -
x + y
-x + y

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