\magnification=\magstep1


$$
    \Delta ({\rm GPE} )  \quad  = \quad {{\rm GPE}_f} - {{\rm GPE}_i}
$$


$$
    {{ \Delta ({\rm GPE} )} \over  {\Delta {\rm height}} }  \quad  
            = \quad 
         { { {{\rm GPE}_f} - {{\rm GPE}_i} } \over {{\rm height}_f - {\rm height}_i} }
$$

$$
    \Delta ({\rm SPE} )  \quad  = \quad {{\rm SPE}_f} - {{\rm SPE}_i}
$$

$$
    {{ \Delta ({\rm SPE} )} \over  {\Delta {\rm length}} }  \quad  
            = \quad 
         { { {{\rm SPE}_f} - {{\rm SPE}_i} } \over {{\rm length}_f - {\rm length}_i} }
$$


\bye
