Tick whether the following statement is true or false.

Give a reason for your answer.

When $n$ is a positive integer, the value of $2n$ is always a factor of the value of $20n$.

True    $□$      False    $□$

Show that $x(x-1)(x+1)={x}^{3}-x$

Prove that ${x}^{2}+x+1$ is always positive.

$n$ is a positive integer.

Prove that $13n+3+(3n-5)(2n+3)$  is a multiple of 6.