the second one is easy: it is given that X^2+Y^2=8XY, thus, X^2+Y^2+2XY=10XY (i.e, added 2XY to both sides) thus, (X+Y)^2 = 10XY. Taking log of both sides: 2

the second one is easy: it is given that X^2+Y^2=8XY, thus, X^2+Y^2+2XY=10XY (i.e, added 2XY to both sides) thus, (X+Y)^2 = 10XY. Taking log of both sides: 2 log (X+Y) = log 10 + log X + log Y = log 5 + log 2 + log X + log Y