plot (1-2* (x^(1)-0.5^(1))/(7^(1)-0.5^(1))*1/x),(1-2*(x^(-1)-0.5^(-1))/(7^(-1)-0.5^(-1))*1/x) ,(1-2*(x^(3)-0.5^(3))/(7^(3)-0.5^(3)) *1/x) from x=0.5 to x=7