How do you multiply ##(3x-2)^2##?

Apply foil method or the short cut method:
Square the first term:
##(3x)^2=9x^2##
Multiply the product of the first and last term by two:
##2(3x)(-2)=-12x##
Square the last term:
##(-2)^2=4##
Combine all the terms: ##9x^2-12x+4##