How do you find the product of (z-5)^2?

${z}^{2} - 10 z + 25$
You can either write ${\left(z - 5\right)}^{2}$ = (z-5)(z-5) and then multip[ly using FOIL, or you can remember the patterns we have for these squared binomials:
${\left(a + b\right)}^{2} = {a}^{2} + 2 a b + {b}^{2}$
${\left(a - b\right)}^{2} = {a}^{2} - 2 a b + {b}^{2}$