If x,y,z>0,$\displaystyle xy\neq1, yz\neq1, zx\neq1$ and $\displaystyle xyz\neq1, then \frac{1}{\log_{xy}(xyz)}$$\displaystyle +\frac{1}{\log_{yz}(xyz)}+\frac{1}{\log_{zx}(xyz)} =$

a)1

b)2

c)3

d)4

I am new to logarithm. I know only the basics. Can anyone tell me from where I can learn logarithm in detail. Thanks in advance.

This question is from the sample paper of my entrance exam I need to learn algorithm to this level so that I can get clear.

I hope someone can help

. Thanks once more time in advance.