Flower Petal Study #3 - Diamond Petal 

This program draws a petal, then turn the turtle so the next petal fits n times around a circle, like slicing a pie into
n pieces so the rotation is 360/ n but while drawing the diamond, the turtle already turns 2a + b degrees where a is the side diamond turn and b is the top diamond turn. This 2a + b internal turn must be accounted for when calculating the turn to the next petal.

So the equation for the petal turn becomes 360/n - (2a + b)