The number of permutations of the letters of the word INSTITUTION are .......

If $x + y = \dfrac{\pi}{4}$, then $(1 + \tan x)(1 + \tan y) =$

A straight line makes equal negative intercepts on the coordinate axes. If the perpendicular distance from the origin to the line is 4 units, then the equation of the line is ......

If the angle made by the lines represented by the equation $ax^2 + 2hxy + by^2 = 0$ with X-axis are $\alpha$ and $\beta$, then $\tan(\alpha + \beta)$ is