If f is homogeneous of degree n, show that fx(tx,ty)=t^(n-1)fx(x,y)
fx: regard y as a constant and differentiate f(x,y)with respect to x.
?f is homogeneous,
? differentiate both sides with respect to x,
Then [df/d(tx)]*[d(tx)/ d(x)]+ [df/d(ty)]*[d(ty)/dx]=t^n*fx(x,y)...