JT
Posts:
1,343
Registered:
4/7/12


Re: Trying to find perimeter of a regular pentagon
Posted:
May 28, 2013 12:03 PM


On 28 Maj, 17:15, 130bcd <carl.sundqu...@gmail.com> wrote: > Hello, > > I have unsuccessfully tried to find the perimeter of a pentagon. The "radius" to the vertices is 130, which I tried to convert into 5 triangles but I can't find a formula for determining the length of the 3rd side of an isosceles triangle. > > The two equal length sides would, of course be 130 and the angle between them would be 72. > > Help, please!
As always you would have to start dividing into two right angled triangles i guess that gives 31 degree angle at centrum, then my trigonometry is to weak to go on from but basicly calculate base and height then multiply using trig formulas and then multiply height 10 times to get the perimeter or ?.
But there is possibly a much easier ratio solution using fractions.

