f(x,y)=x^t * y^m - (x+y)^(m+t)=0f(x,y)=xt⋅ym−(x+y)m+t=0
df = f_xdx+f_ydy=0df=fxdx+fydy=0 so
dy/dx=-f_x/(f_y)dydx=−fxfy but
f_x=t/x x^ty^m-(t+m)/(x+y)(x+y)^(t+m)fx=txxtym−t+mx+y(x+y)t+m
and
f_y=m/y x^ty^m-(t+m)/(x+y)(x+y)^(t+m)fy=myxtym−t+mx+y(x+y)t+m
but
x^ty^m=(x+y)^(t+m)xtym=(x+y)t+m then
f_x=(t/x-(t+m)/(x+y))x^ty^mfx=(tx−t+mx+y)xtym and
f_y=(m/y-(t+m)/(x+y))x^ty^mfy=(my−t+mx+y)xtym
so
dy/dx=-(t/x - (t + m)/(x + y))/(m/y - (t + m)/(x + y))=y/xdydx=−tx−t+mx+ymy−t+mx+y=yx