Who many diagonals does a rectangle have?

Answer 1

2 Pentagon-5

Hexagon - 9

formula

diagonals=(n-3)+sum from i=1->i=(n-3) [i]

diagonals=(n-3)+1+2+. . .+(n-3)

The n-3 is because you cannot draw lines to a same point or adjacent ones.

The reason (n-3) is used twice, is because the first 2 points you start to draw from are not connected to each other so they draw all the lines they can.

Once you get to the third (assuming you are moving in a circle), the number of lines you can draw is reduced by 1, since that line is already drawn (to the first point). The 4th one now already has a line to the first and second points and so draws 2 less lines.