The area of a regular polygon with a side of 11 cm is 247.5 cm². If the perpendicular distance from the centre to the side of the polygon is 9 cm, what is the number of sides of the polygon?
5
Area of a regular polygon: \(\dfrac12\times\text{perimeter}\times\text{apothem}\).
With side=11 cm, apothem=9 cm, and n sides: \(\dfrac12\times(11n)\times9 = 247.5\).
\(49.5n = 247.5 \Rightarrow n = 5\).
Hence, the polygon has 5 sides.
The shorter side of a rectangle is 15 cm less than the longer side. The numerical value of its area is equal to 5 times the numerical value of its perimeter. What is the length (in cm) of its longer side?