负5除以负9分之7乘以5分之4乘以负2又4分之1除

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负5除以负9分之7乘以5分之4乘以负2又4分之1除以7
=-5/(-7/9)*4/5*(-9/4)/7
=-5*9/7*4/5*9/4*1/7
=-9*9/(7*7)
=-81/49