Factorise the following:
$9 y^{2}-66 y z+121 z^{2}$

(N/A) We have the expression $9 y^{2}-66 y z+121 z^{2}$.
This can be written in the form $a^{2}-2 a b+b^{2} = (a-b)^{2}$.
$9 y^{2}-66 y z+121 z^{2} = (3 y)^{2} - 2(3 y)(11 z) + (11 z)^{2}$.
Comparing this with the identity $(a-b)^{2} = a^{2}-2 a b+b^{2}$,where $a = 3 y$ and $b = 11 z$.
Therefore,$9 y^{2}-66 y z+121 z^{2} = (3 y - 11 z)^{2}$.
This can be written as $(3 y - 11 z)(3 y - 11 z)$.