Question
If the coefficient of ${x^7}$ in ${\left( {ax - {1 \over {b{x^2}}}} \right)^{13}}$ and the coefficient of ${x^{ - 5}}$ in ${\left( {ax + {1 \over {b{x^2}}}} \right)^{13}}$ are equal, then ${a^4}{b^4}$ is equal to :
If the coefficient of ${x^7}$ in ${\left( {ax - {1 \over {b{x^2}}}} \right)^{13}}$ and the coefficient of ${x^{ - 5}}$ in ${\left( {ax + {1 \over {b{x^2}}}} \right)^{13}}$ are equal, then ${a^4}{b^4}$ is equal to :