We Have,
#color(white)(xxx)a^(2x - 3) * b^(2x) = a^(6-x) * b^(5x)#
#rArr a^(2x - 3)/a^(6-x) = b^(5x)/b^(2x)#
[Just Transpose the #a# and #b# on their respective sides.]
#rArr a^((2x - 3)-(6 - x)) = b^(5x - 2x)# [As #a^(m-n) = a^m/a^n#]
#rArr a^(2x - 3 - 6 +x) = b^(3x)#
#rArr a^(3x - 9) = b^(3x)#
#rArr (a^(x - 3))^3 = (b^x)^3# [As, #(x^m)^n = x^(mn)#]
#rArr a^(x - 3) = b^x#
#rArr a^x/a^3 = b^x# [As #a^(m-n) = a^m/a^n#]
#rArr a^x/b^x = a^3# [Transposing again]
#rArr (a/b)^x = a^3# [As #(a/b)^m = a^m/b^m#]
#rArr log (a/b)^x = log a^3# [Taking #log# at both sides]
#rArr x log (a/b) = 3 log a# [As #log a^x = x log a#]
#rArr 3 log a = x log (a/b)#
Hence Proved.