We are comparing areas, so square of the linear dimension Relative cost per unit area 12^2/6=24 16^2/10=256/10=25.6 Since 24<25.6, the 12" pizza is a better deal.
Note: we could compare exact area by calculating A=pi (d^2)/4, but since it is a relative comparison, the result will be the same, albeit more work.
The angle at A made by the radius and the tangent is 90°. The angle at O is the same as arc AB, 64°. The acute angles in a right triangle are complementary, so the angle at C is the complement of 64°.
