Concept of componendo and dividendo to be used
Given: 5x+6y5u+6v=5x−6y5u−6v
When you replace the denominator of the first ratio with the numerator of the second ratio,the two ratio remains proportional to each other,
If a:b=c:d, then a:c=b:d
So, 5x+6y5u+6v=5x−6v5u−6v
⇒5x+6y+5x−6y5x+6y−5x+6y=5u+6v+5u−6v5u+6v−5u+6v
⇒10x12y=10u12v
⇒xy=uv
⇒x:y=u:v
Hence,proved.