εf,x = f ' (x) * x / f(x) = (1+2x)*x / ((x+x^2) = (1+2x)*x / (x*(1+x)) = (1+2x) / (1+x) = (q+x + x) / (1+x) = 1 + x/(1+x)
bei g(x) = (x-1)/(x+1) ist g ' (x) =( (x+1)*1 - (x-1) * 1 ) / (x+1)^2 Quotientenregel
= 2/ (x+1)^2
also εg,x = g ' (x) * x / g(x) = ( 2/ (x+1)^2 ) * x / ( (x-1)/(x+1) )
= ( 2 * x * (x+1) ) / ((x+1)^2 * (x-1) )
= ( 2 * x *) / ((x+1) * (x-1) ))
= ( 2 * x *) / (x^2 -1)