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.