(a)visibility=\(\frac{2 \sqrt{I_1 I_2}}{I_1+I_2}=\frac{2E_{01} E_{02}}{E_{01}^2+E_{02}^2}=\frac{2E_{01} E_{02}}{E_{01}^2+E_{02}^2} \frac{\frac{1}{E_{02}^2}}{\frac{1}{E_{02}^2}}=\frac{2R}{R^2+1}\)

\(R=\frac{E_{01}}{E_{02}}\)

\(R=2\), visibility=\(\frac{2(2)}{(2)^2+1}=0.8\)

(b)vibility=\(0.5=\frac{2R}{R^2+1}\)

\(R^2-4R+1=0\)

\(R=\frac{4 \pm \sqrt{16-4}}{2}=2 \pm \sqrt{3}\)

\(R=2+\sqrt{3}=3.732\)

\(R=2-\sqrt{3}=\frac{1}{2+\sqrt{3}}=\frac{1}{3.732}\)