How do you find the zeroes for #y=(x-9)^2#?
Just solve the inner equation.
When you want to find the zeroes of a function, you have to match its image to 0.
In this case you'll have
And when you have a product of binomials equal to zero, you can match the interior of each binomial to zero no matter the index, and you will automatically find the solutions or the zeroes.
Here you can't get it easier: