Which one of the following is a square root of $\rm 2a+2\sqrt{a^2 + b^2}$, where a, b ∈ ℝ?

If sinθ and cosθ are the roots of the equation ax² + bx + c = 0, then which one of the following is correct?

If C(n, 4), C(n, 5) and C(n, 6) are in AP, then what is the value of n?

How many 4 - letter words (with or without meaning) containing two vowels can be constructed using only the letters (without repetition) of the word 'LUCKNOW'?