Question 66014
The lengths of the sides doesn't matter.  What matters here is the interior angle and how many sides there are.  The formula for this is:


{{{ k = ((n-2)/n)180 }}}
k = interior angle = 160
n = number of sides
{{{ 160 = ((n-2)/n)180 }}}
Divide both sides by 180
{{{ 160/180 = (n-2)/n }}}
reduce the left side
{{{ 8/9 = (n-2)/n }}}
Cross multiply
{{{ 9(n-2) = 8n }}}
Distribute
{{{ 9n - 18 = 8n }}}
add 18 to both sides
{{{ 9n = 8n + 18 }}}
subtract 8n from both sides
{{{ n = 18 }}}
n = number of sides = 18