Wie vereinfacht man # ((5a) / (3b)) ^ - 2 #?

# ((5a) / (3b)) ^ - 2 #
# = 1 / ((5a) / (3b)) ^ 2 #
# = ((3b) / (5a)) ^ 2 #
# = ((3b) ^ 2) / (5a) ^ 2 #
# = (3 ^ 2b ^ 2) / (5 ^ 2a ^ 2) #
# = (9b ^ 2) / (25a ^ 2) #