Question 1147738
side length of octagon = s


{{{s/(sqrt(2)) + s + s/(sqrt(2)) = 12}}}
{{{sqrt(2) * s + s = 12}}}
{{{s(1 + sqrt(2)) = 12}}}
{{{s = 12/(1 + sqrt(2))}}}
{{{s = 12 * sqrt(2) - 12}}}


area of four triangles cut off = {{{4 * ((s/sqrt(2))^2)/2 = s^2}}}


{{{s^2 = 432 - 288 * sqrt(2) = 24.706}}} cm^2