Question 998939
.
{{{(cos(y))/(1-tan(y))}}} + {{{(sin(y))/(1-cot(y))}}} = {{{(cos(y))/(1 - (sin(y)/(cos(y))))}}} + {{{(sin(y))/(1 - (cos(y)/(sin(y))))}}} = {{{(cos(y))/(((cos(y) - sin(y))/(cos(y))))}}} + {{{(sin(y))/(((sin(y) - cos(y))/(sin(y))))}}} = {{{(cos^2(y))/(cos(y) - sin(y))}}} + {{{(sin^2(y))/(sin(y) - cos(y))}}} = 


{{{(cos^2(y))/(cos(y) - sin(y))}}} - {{{(sin^2(y))/(cos(y) - sin(y))}}} = {{{(cos^2(y) - sin^2(y))/(cos(y) - sin(y))}}} = {{{((cos(y) - sin(y))*(cos(y) + sin(y)))/(cos(y) - sin(y))}}} = {{{(cross((cos(y) - sin(y)))*(cos(y) + sin(y)))/(cross((cos(y) - sin(y))))}}} = cos(y) + sin(y).


It is what has to be proved.