undecagon has 43 diagonals (answer by erwin handsome)
54
1/2*(152-45) = 90 diagonals
Two.
There are zero diagonals in a circle because a circle has no sides no vertices or it doesn't have a flat surface so zero.
Use the equation n(n-3) / 2 Where n = number of sides So, 40(40 - 3) / 2 = 740
How to Do Diagonal Raise
How to Train for Diagonal Strength in Tennis
How to Make a Diagonal Stitch in Loom Knitting
How to Use Cross Hatching Diagonals