If a function $\mathrm { f } : [ - 2 \mathrm { a } , 2 \mathrm { a } ] - - > \mathrm { R }$ is an odd function such that $\mathrm { f } ( \mathrm { x } ) = \mathrm { f } ( 2 \mathrm { a } - \mathrm { x } )$ for $\mathrm { x } \hat { \mathrm { I } } [ \mathrm { a } , 2 \mathrm { a } [$ and the left hand derivative at $\mathrm { x } = \mathrm { a }$ is 0 then find the left hand derivative at $\mathrm { x } = - \mathrm { a }$.