Find area of reg. pentagon w/ s = 7 and apothem of 4.8

[JayJay06]

May someone help with this problem.

Find the area of a regular pentagon with sides 7 millimeters long and apothem 4.8 mm long. (A= 1/2aP).

Thank you for the help.

 

[stapel]

In your formula, what do "a" and "P" stand for?

How far have you gotten in applying the formula(s) you've been given?

Please be specific. Thank you.

Eliz.

 

[JayJay06]

I think my answer is:

P= 5s
P= 5(7)
P= 35

A= 1/2 (4.8)(35)
A=84

Is that right?

 

[Denis]

JJ, 84 is correct as the total area of 5 triangles with base=7 and height=4.8

However, that is NOT a pentagon.
Plus you don't need the apothem's length to calculate area of a pentagon.

What grade are you in? Is that a problem made up by your teacher?
Without going in any details, the area of a pentagon sides=7 is 84.30339....
Area can be calculated this way: 5s^2 / (4TAN(36)) where s = side length.

Tell your teacher the apothem = 4.817336...., NOT 4.8 :shock:

Btw, the formula 1/2(AP) means half the product of Apothem times Perimeter

 

[JayJay06]

Thank you for the help.