If $x^{2}-8 x-20=(x+a)(x+b),$ then $a b=\ldots \ldots \ldots$

The degree of polynomial $5 x^{2}-7 x-11$ is..........

One of the factors of $\left(25 x^{2}-1\right)+(1+5 x)^{2}$ is

Evaluate the following using suitable identities

$(105)^{3}$

Factorise

$16 x^{2}-40 x y+25 y^{2}$

Multiply $x^{2}+4 y^{2}+z^{2}+2 x y+x z-2 y z$ by $(-z+x-2 y)$