Question 4297
This question can be answered either by "discovery" or by "construction."


For discovery method, consider a rectangle, which has four sides and one diagonal from a given vertex.


Next consider a pentagon, which has five sides and (picture it!) two diagonals from a given vertex.


Consider a hexagon, which has 6 sides, and each additional side adds an additional diagonal from each given vertex, which would be 3 diagonals.


Did you notice the pattern?  The number of diagonals from a given vertex is 3 less than the number of vertices.  The question at hand is for a decagon, which is a 10 sided figure, so there would be 10-3 or 7 diagonals from a given vertex.


Finally, you could always draw a 10 sided figure, draw all the diagonals from a given vertex, and count them for yourself!!


R^2 from SCC