geometry
posted by Katie .
what is the length of any diagonal of a regular pentagon with a side of 20mm ?

what is the length of any diagonal of a regular pentagon with a side of 20mm

first find the size of each interior angle
angle = 180(52)/5 = 108°
let the length of the diagonal be x
by cosine law
x^2 = 20^2 + 20^2 2(20)(20)cos 108°
I am sure you can finish it from there.