Areas, Surface Areas, and Volumes Unit Areas of Regular Polygons
Things to Remember Trig Ratios : Angles of a Polygon Remember: 30-60-90 triangles shortcuts H = (SL ) 2 LL = ( SL )√ 3 Trig Ratios : Angles of a Polygon
Terms to Know: Any regular polygon: Radius: is a segment joining the center to any vertex Apothem: is a segment joining the center to the midpoint of any side and is also perpendicular to the side.
Area of a regular polygon: Remember all angles are congruent and all sides are congruent. N Regular pentagon: O is the center OA the radius OM is an apothem O T E P M A
Apothems Facts: All apothems of a regular polygon are congruent. Only regular polygons have apothems. An apothem is the perpendicular bisector of a side.
A reg. poly = ½ a p Where : a = apothem p = perimeter Area of a regular polygon equals one-half the product of the apothem and the perimeter. Where : a = apothem p = perimeter
A regular polygon has a perimeter of 40 cm and an apothem of 5 cm A regular polygon has a perimeter of 40 cm and an apothem of 5 cm. Find the polygon’s area. A = ½ap = ½(5)(40) = 100 cm2
Find the area of a regular hexagon whose sides are 18 cm long. Draw the picture Write the formula Plug in the numbers Solve and label units
A = ½ ap A = ½ (9√3)108 A = 486√3 cm 2 18cm P = 18(6) = 108 cm Find the perimeter Find each angle Find the apothem 18cm P = 18(6) = 108 cm Angles = 720º/6 angles = 120º per angle Radius breaks it into 60º angles. 30-60-90 triangle, apothem = 9√3 cm Write the formula, and solve. A = ½ ap A = ½ (9√3)108 A = 486√3 cm 2