Let {x} and [x] denote the fractional part of x and
the greatest integer $$ \le $$ x respectively of a real
number x. If $$\int_0^n {\left\{ x \right\}dx} ,\int_0^n {\left[ x \right]dx} $$ and 10(n² – n),
$$\left( {n \in N,n > 1} \right)$$ are three consecutive terms of a G.P., then n is equal to_____.

Let PQ be a diameter of the circle x² + y² = 9. If $$\alpha $$ and $$\beta $$ are the lengths of the perpendiculars from P and Q on the straight line,
x + y = 2 respectively, then the maximum value of $$\alpha\beta $$ is _____.

A test consists of 6 multiple choice questions, each having 4 alternative answers of which only one is correct. The number of ways, in which a candidate answers all six questions such that exactly four of the answers are correct, is __________.

The function
$$f(x) = \left\{ {\matrix{ {{\pi \over 4} + {{\tan }^{ - 1}}x,} & {\left| x \right| \le 1} \cr {{1 \over 2}\left( {\left| x \right| - 1} \right),} & {\left| x \right| > 1} \cr } } \right.$$ is :