Binomial Theorem

If the coefficient of \({x^7}\) in \({\left( {a{x^2} + {1 \over {2bx}}} \right)^{11}}\) and \({x^{ - 7}}\) in \({\left( {ax - {1 \over {3b{x^2}}}} \right)^{11}}\) are equal, then :