There is a problem with your question.
You said it was a regular octagon with sides 19 inches, forget the apothem part right now.
Then you have 8 equal isosceles triangles with an angle of 360/8 or 45° at the top and angles of 67.5° at each of the bases.
The height of one of those triangles is:
sin 67.5° = h/9.5
h = 9.5sin67.5 = 8.776... , certainly not 16
They were tempting you to say:
Each of the 8 triangles has area of
(1/2)(19)(16)
= 152 inches^2
so the total area = 8(152) or 1216 inches^2
which was one of the choices, but not correct
The question is bogus!!!
Where did you get it ?
1. What is the area of a regular octagon with an apothem 16 inches long and a side 19 inches long? Round the answer to the nearest inch.
A) 144 in^2
B) 216 in^2
C) 1,216^2
D) 2432 in^2
Is the answer D? That's what I solved it.
5 answers
I agree with you! It's on one of my small worksheets and I'm absolutely confused. I'll show you how I came up with 2432 while using the formula I was told to use.
Area= Perimeter x Apothem.
19*8*16= 2423.
I'm confused. Is that not the answer then? Should it be 1216. It seems this question has multiple answers, but not correct ones.
Area= Perimeter x Apothem.
19*8*16= 2423.
I'm confused. Is that not the answer then? Should it be 1216. It seems this question has multiple answers, but not correct ones.
I think you missed my point.
I was pointing out that there is no octagon possible with sides of 19 and apothem of 16.
Carefully read what my explanation said.
Thus, none of the answers make any sense.
Please let your teacher know, so he/she can correct the worksheet.
Just because we can do the arithmetic of a formula doesn't mean it is correct.
I was pointing out that there is no octagon possible with sides of 19 and apothem of 16.
Carefully read what my explanation said.
Thus, none of the answers make any sense.
Please let your teacher know, so he/she can correct the worksheet.
Just because we can do the arithmetic of a formula doesn't mean it is correct.
To find the area of any regular (regular means all sides are = and all angles are =) polygon when you know the length of the apothem and the length of the side you can use the formula:
A = (1/2)ap where a = the length of the apothem and p = the perimeter of the polygon. You can also use n*s in place of p where n = the number of sides of the polygon and s = the length of the side.
A= (1/2)(16)(19*8) (An octagon has 8 sides.)
A = 1216 in^2
A = (1/2)ap where a = the length of the apothem and p = the perimeter of the polygon. You can also use n*s in place of p where n = the number of sides of the polygon and s = the length of the side.
A= (1/2)(16)(19*8) (An octagon has 8 sides.)
A = 1216 in^2
1216
I know this is a few years later but the answer is...
as Na Jaemin said! i had it on a test and that was the correct answer!
I know this is a few years later but the answer is...
as Na Jaemin said! i had it on a test and that was the correct answer!
1 answer