<span>x^2-xy-x+y=0
х</span>²-х- ху+у=0
х(х-1)-у(х-1)=0
х(х-1)= у(х-1)
у = х(х-1)/(х-1)
у=х
Решение во вложении
--------------------------------------
<span>sin(-a+П) = sina</span>
<span><span>cos(П-a) = -cosa</span></span>
<span><span><span>sin(a-7Пи)=-sina</span></span></span>
<span><span><span>cos(a-9П) = -cosa</span></span></span>