lg √45
=1/2×lg 45
=1/2×lg(5×3×3)
=1/2×lg 5+lg 3
=1/2×lg(10÷2)+lg 3
=1/2×(lg10 - lg 2)+lg 3
=1/2 × (1 - a) + b
= - a/2 +b +1/2