(x+y)^1/2+(y-x)^1/2=c

thus diff both sides wrt x we get

(1+y' )/ 2*(x+y)^1/2 +(y ' -1)/2*(x+y)^1/2 =0.................since c is a constant

thus u get y' =[(x+y)^1/2- (y-x)^1/2]/[(x+y)^1/2+(y-x)^1/2]

then take d second derivative ......(itz tedious bt u get d answer )

and substitute ( x+y)^1/2+(y-x)^1/2=c.........

and there u r wid ur ansewr ..........