If a2+4b2=12ab, then log (a + 2b) is
12[log a+log b−log 2]
loga2+logb2+log2
12[log a+log b+4log 2]
12[log a−log b+4 log 2]
a2+4b2+4ab=16ab ∴ (a+2b)2=16ab ∴ 2log(a+2b)=4log 2+log a+log b
Therefore log (a +2b) = 12(4log2+loga+logb)
If a-2b = 15 and find a2+ 4b2 .