lg5 X lg20 - lg2 X lg50 - lg25

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lg5 X lg20 - lg2 X lg50 - lg25
lg5 X lg20 - lg2 X lg50 - lg25

lg5 X lg20 - lg2 X lg50 - lg25
注意lg2+lg5=lg10=1
lg5 X lg20 - lg2 X lg50 - lg25
  = lg5 X (lg2+lg10)-lg2 X (lg5+lg10)-2lg5
  = lg5 X lg2+lg5-lg2 X lg5-lg2-2lg5
  =-lg5-lg2
  =-lg10
  =-1