x2 + y2 = 25xy
Adding 2xy on both sides
x2 + y2 + 2xy = 25xy + xy
(x + y)2 = xy
log(x + y)2 = logxy
2 log(x + y) = log3xy
2 log(x + y) = log3+ logx + logy
2 log(x + y) = 3log+ logx + logy