Four geometric means are inserted between $\;2^{9}-1\;and \;2^{9}+1\;.$ The product of these means is :

Question

$(a)\;2^{36}-1\qquad(b)\;2^{36}-2^{19}+1\qquad(c)\;2^{36}-2^{18}+1\qquad(d)\;None\;of\;these$