(1+1/3+1/5+1/7)(1/3+1/5+1/7+1/9)-(1+1/3+1/5+1/7+1/9)(1/3+1/5+1/7)
=(1/3+1/5+1/7+1/9)+(1/3+1/5+1/7)*(1/3+1/5+1/7+1/9)—(1/3+1/5+1/7)-(1/3+1/5+1/7+1/9)*(1/3+1/5+1/7)
=(1/3+1/5+1/7+1/9)-(1/3+1/5+1/7)
=1/9
(1+1/3+1/5+1/7)(1/3+1/5+1/7+1/9)-(1+1/3+1/5+1/7+1/9)(1/3+1/5+1/7)
=(1/3+1/5+1/7+1/9)+(1/3+1/5+1/7)*(1/3+1/5+1/7+1/9)—(1/3+1/5+1/7)-(1/3+1/5+1/7+1/9)*(1/3+1/5+1/7)
=(1/3+1/5+1/7+1/9)-(1/3+1/5+1/7)
=1/9