$\left| {\,\begin{array}{*{20}{c}}{a + b}&{a + 2b}&{a + 3b}\\{a + 2b}&{a + 3b}&{a + 4b}\\{a + 4b}&{a + 5b}&{a + 6b}\end{array}\,} \right|\, = \,\left| {\,\begin{array}{*{20}{c}}{a + b}&{a + 2b}&{a + 3b}\\b&b&b\\{2b}&{2b}&{2b}\end{array}\,} \right| = 0$
$\left\{ {{\rm{by }}\begin{array}{*{20}{c}}{{R_2} \to {R_2} - {R_1}}\\{{R_3} \to {R_3} - {R_2}}\end{array}} \right\}$
Trick : Putting $a = 1 = b$. The determinant will be $\left| {\,\begin{array}{*{20}{c}}2&3&4\\3&4&5\\5&6&7\end{array}\,} \right| = 0$. Obviously answer is $ (d)$
Note : Students remember while taking the values of $a,\,b,\,\,c,.......$ that for there values, the options $(a), (b), (c) $ and $(d) $ should not be identical.
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If $1,\omega ,{\omega ^2}$ are the cube roots of unity, then $\Delta = \left| {\,\begin{array}{*{20}{c}}1&{{\omega ^n}}&{{\omega ^{2n}}}\\{{\omega ^n}}&{{\omega ^{2n}}}&1\\{{\omega ^{2n}}}&1&{{\omega ^n}}\end{array}\,} \right|$ is equal to