Largest number among the given numbers How to find the largest number among the following numbers.
$(a)\;3^{210}$
$(b)\;7^{140}$
$(c)\;17^{105}$
$(d)\;31^{84}$
Any help will be greatly appreciated.

Note that $.3^{210}=(.3^2)^{105}=.09^{105}<.17^{105}$.
Also $.31^{84}>.17^{84}>.17^{105}$ and
finally $.7^{140}=(.7^2)^{70}=.49^{70}>.31^{70}>.31^{84}$. Hence
$$ .7^{140}> .31^{84}>.17^{105}>.3^{210}$$
