If $${\log _3}\,2\,,\,\,{\log _3}\,({2^x} - 5)\,,\,and\,\,{\log _3}\,\left( {{2^x} - {7 \over 2}} \right)$$ are in arithmetic progression, determine the value of x.

Line $$L$$ has intercepts $$a$$ and $$b$$ on the coordinate axes. When the axes are rotated through a given angle, keeping the origin fixed, the same line $$L$$ has intercepts $$p$$ and $$q$$, then

Straight lines $$3x + 4y = 5$$ and $$4x - 3y = 15$$ intersect at the point $$A$$. Points $$B$$ and $$C$$ are choosen on these two lines such that $$AB = AC$$. Determine the possible equations of the line $$BC$$ passing through the point $$(1, 2)$$.

A line cuts the $$x$$-axis at $$A (7, 0)$$ and the $$y$$-axis at $$B (0, -5)$$. A variable line $$PQ$$ is drawn perpendicular to $$AB$$ cutting the $$x$$axis in $$P$$ and they $$Y$$-axis in $$Q$$. If $$AQ$$ and $$BP$$ intersect at $$R$$, find the locus of R.