If cosy=xcos(a+y). And dx/dy =k/1+(x)2-2xcosa...... Then find value of k Now my main question is..For above que. We should diff. w.r.t "y" and we get k=sina.. ..And i see same que in diff book like this mainor.. .... If cosy=xcos(a+y). And dy/dx =k/1+(x)2-2xcosa...... Then find value of k ,and for this we should diff w.r.t "x"..And we get same ans. K=sina then for this que. We prove dy/dx=dx/dy... Thanks