log2根号下48分之7+log2 12-log2 42
=log2 (√(7/48) *12/42)
=log2 (√21/3 *2/7)
=log2 (2√(21/3*49))
=log2 (2√7 /7)
=log2 2 +log2 7^(-1/2)
=1- 1/2log2 7