Which from following plants is useful to extract analgesic compound from it ?

The difference between the roots of the equation $x^2 + 2x + 4 = 0$ is $\ldots$ (where $i = \sqrt{-1}$)

In a test, there are 7 questions of the type 'True or False'. No student got all the answers correct. If the sequence of answers for every student is unique, then the maximum number of students who appeared for the test is $\ldots$

Let $f_k(x) = \dfrac{1}{k}(\cos^k x + \sin^k x)$ where $k \in N$, then $f_6(x) - f_4(x) = \ldots$