lg5 X lg20 - lg2 X lg50 - lg25
问题描述:
lg5 X lg20 - lg2 X lg50 - lg25
答
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