Log2√（7/48） +log2 12 -（1/2）log2 42

log2√(7/48)+log2 12 -1/2log2 42
=log2√(7/48)+log2(12)-log2√42
=log2√(7/48)*12/√42
=log2√7*144/48*42
=log2√(1/2)
=1/2log2(1/2)
=-1/2