Question 769201
Hard to draw the figure in a reliable way, so describing.


C is the center point of pizza, P is a point on the edge, make an angle 120 degrees from P to another point M.  In middle of P and M is point D.  


CP is 18 inches
Triangle CDP is a  30-60-90 triangle and angle CDP is 90 degrees.  Angle PCD is 60 degrees.  Triangle is half of a equilateral triangle, so CD is 4&1/4 inches.


Use pythagorean theorem, {{{DP=sqrt(9^2-(9/2)^2)}}}
{{{DP=(9/2)sqrt(3)}}}


Area of the slice then is, since there are three triangles with the central angle of 120 degrees, {{{3*(9/2)((9/2)sqrt(3))}}}
Which is like {{{(1/2)*CD*DP}}} AND THEN MULTIPLY BY 6.


Area of the original pizza was {{{pi*9^2}}}