Prove that the square of any positive integer is of the form $3m$ or $3m+1$ but not of the form $3m+2.$

Check whether $6^n$ can end with the digit $0$ for any natural number $n$.

Show that every positive odd integer is of the form $\left(4q+1\right)$ or $\left(4q+3\right)$, where $q$ is some integer.

Solve the quadratic equation $x^2-9=0.$

The HCF of two co-prime numbers is :

If $\mathrm{A}$ is integer, $\mathrm{B}$ is natural number then $\mathrm{B}-\mathrm{A}=?$