' If `a=x/(x+y)`and `b=y/(x-y)`, then `(a b)/(a+b)`is equal to(a) `(x y)/(x^2+y^2)`(b)

" If `a=x/(x+y)`
and `b=y/(x-y)`
, then `(a b)/(a+b)`
is equal to
(a) `(x y)/(x^2+y^2)`
(b) `(x^2+y^2)/(x y)`
(c) `x/(x+y)`
(d) `(y/(x+y))^2`"