#(1+cos(pi/8))(1+cos((3pi)/8))(1+cos((5pi)/8))(1+cos((7pi)/8))#
#=(1+cos(pi/8))(1+sin(pi/2-(3pi)/8))(1+sin(pi/2-(5pi)/8))(1+cos(pi-pi/8))#
#=(1+cos(pi/8))(1+sin(pi/8))(1-sin(pi/8))(1-cos(pi/8))#
#=(1-cos^2(pi/8))(1-sin^2(pi/8))#
#=sin^2(pi/8)cos^2(pi/8)#
#=1/4xx(2sin(pi/8)cos(pi/8))^2#
#=1/4xxsin^2((2pi)/8)#
#=>1/4xxsin^2(pi/4)#
#=1/4xx(1/sqrt2)^2#
#=1/8#