Evaluate $(421)^{2}$.

Factorise $4 x^{2}+9 y^{2}+49 z^{2}-12 x y+42 y z-28 z x$.

With the help of the remainder theorem,examine whether $x+2$ is a factor of the polynomial $x^{3}+9x^{2}+26x+24$ or not.

Find $p(1)$,$p(2)$,and $p(4)$ for the following polynomial:
$p(x) = x^{2} - 3x + 2$

The polynomial $p(x) = x^{4} - 2x^{3} + 3x^{2} - ax + 3a - 7$ when divided by $x + 1$ leaves the remainder $19$. Find the value of $a$. Also,find the remainder when $p(x)$ is divided by $x + 2$.

For $p(x) = x^{3} + 9x^{2} + 26x + 24$,find the value of $p(-2)$.