If f(x,y)=cos−1{1−xy√1+x2√1+y2}, then fx=
Let f(x,y)=√x2+y2+√x2+y2−2x+1+√x2+y2−2y+1+√x2+y2−6x−8y+25∀x,yϵR, then
Find the value of tan [12{sin−1(2x1+x2)+cos−1(1−y21+y2)}],|x|<1,y>0,xy<1 .