赞 sore2003 幼苗
共回答了18个问题采纳率：94.4% 举报
（1）原式=(1/2)*[log2 (7/48)] - (1/2)*(log2 42)+ (log2 12)
=(1/2)*[log2 (7/48) - (log2 42)]+ (log2 12)
=(1/2)*{log2 [(7/48)÷42]} + (log2 12)
=(1/2)*{log2 [1/(6*48)]} + (log2 12)
=-(1/2)*[log2 (4*9*8)] + 2+(log2 3)
=-(1/2)*(5+ log2 9)+ 2+(log2 3)
=(-5/2) - (log2 3)+ 2+(log2 3)
=-1/2
（2）原式=2lg5 + 2lg2+ lg5*(2lg2 + lg5)+(lg2)²
=2+ （lg5)²+2*lg5*lg2+(lg2)²
=2+（lg5+lg2）²
=2+1=3
=(1/2)*[log2 (7/48) - (log2 42)]+ (log2 12)
=(1/2)*{log2 [(7/48)÷42]} + (log2 12)
=(1/2)*{log2 [1/(6*48)]} + (log2 12)
=-(1/2)*[log2 (4*9*8)] + 2+(log2 3)
=-(1/2)*(5+ log2 9)+ 2+(log2 3)
=(-5/2) - (log2 3)+ 2+(log2 3)
=-1/2
（2）原式=2lg5 + 2lg2+ lg5*(2lg2 + lg5)+(lg2)²
=2+ （lg5)²+2*lg5*lg2+(lg2)²
=2+（lg5+lg2）²
=2+1=3
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