左(frac { l ^ alpha }{1-left (frac { l }{ h } right) ^ alpha } cdot left (frac { alpha }{ alpha-2} right) cdot left (frac {1}{ l ^ { alpha-2}-frac {1}{ h ^ { alpha-2}} right) ,alpha neq 2 | 左(frac { l ^ alpha }{1-left (frac { l }{ h } right) ^ alpha } cdot left (frac { alpha }{ alpha-2} right) cdot left (frac {1}{ l ^ { alpha-2}-frac {1}{ h ^ { alpha-2}} right) ,alpha neq 2 |