If x13 y7 = (x + y)20, prove that 
Here,
x13 y7 = (x + y)20
Taking log on both sides,
13 log x+7log y = 20 log(x+y)
[ Since, log (AB)=logA+logB ; log 
=b log a]
Differentiating it with respect to x using the chain rule,
Hence, Proved.
33
If x13 y7 = (x + y)20, prove that
Here,
x13 y7 = (x + y)20
Taking log on both sides,
13 log x+7log y = 20 log(x+y)
[ Since, log (AB)=logA+logB ; log =b log a]
Differentiating it with respect to x using the chain rule,
Hence, Proved.