The sum of the series $${1 \over {1.2}} - {1 \over {2.3}} + {1 \over {3.4}} - \,\,.....\,\,\infty $$ is

If $${\log _3}x + {\log _3}y = 2 + {\log _3}2$$ and $${\log _3}(x + y) = 2$$, then

If $${\log _7}2 = \lambda $$, then the value of $${\log _{49}}(28)$$ is

The sequence log a, $$\log {{{a^2}} \over b}$$, $$\log {{{a^3}} \over {{b^2}}}$$, ...... is