If $x + \sqrt{x^2 + 1} = a$,then $x =$

$A$ man running round a race-course notes that the sum of the distances of two flag-posts from him is always $10 \ m$ and the distance between the flag-posts is $8 \ m$. The area of the path he encloses in square metres is (in $\pi$)

In a gene bank,in what form is the genetic material stored?

Which of the following statements is correct?

Let $z = a - \frac{i}{2}$,where $a \in R$. Then $|i + z|^2 - |i - z|^2$ is equal to

Which of the following is correct for $Chlorophyceae$?