If $n$ is a positive integer, then $(1 + i\sqrt{3})^{2n} + (1 - i\sqrt{3})^{2n}$ is equal to .........

The number of 4-letter words formed from the English alphabet such that there are exactly 2 vowels and 2 consonants and no vowel is repeated, but consonants may be repeated is:

The value of $\cos(60^\circ - A)\cdot\cos A\cdot\cos(60^\circ + A)$ is

The general solution of the equation $\cot\theta \cdot \cot 2\theta = 1$ is...