71. (1 + sin 2alpha) / cos 2alpha = tg (pi/4 + alpha);

(1 + sin 2alpha) / cos 2alpha = (sin^2 alpha + cos^2 alpha + 2 sin alpha cos alpha) / (cos^2 alpha - sin^2 alpha) = (sin alpha + cos alpha)^2 / ((cos alpha - sin alpha)(cos alpha + sin alpha)) = (sin alpha + cos alpha) / (cos alpha - sin alpha) = (tg alpha + 1) / (1 - tg alpha) = tg (pi/4 + alpha).