Expand: $(3x + 7y)(3x - 7y)$

If the polynomials $az^{3}+4z^{2}+3z-4$ and $z^{3}-4z+a$ leave the same remainder when divided by $z-3$,find the value of $a$.

Factorise:
$2 x^{2}-7 x-15$

Expand the following:
$(3a - 2b)^3$

Which of the following expressions are polynomials in one variable and which are not? State reason for your answer. If the given expression is a polynomial,state whether it is a polynomial in one variable or not: $x^{2}-8x+15$

Expand $\left(\frac{x}{2}-\frac{2}{5}\right)^{2}$.