Question 17
The expression
$$
\frac{\dfrac{a}{a+y}+\dfrac{y}{a-y}} {\dfrac{y}{a+y}-\dfrac{a}{a-y}},
$$
$a$ real, $a\ne0,$ has the value $-1$ for:
$$
\frac{\dfrac{a}{a+y}+\dfrac{y}{a-y}} {\dfrac{y}{a+y}-\dfrac{a}{a-y}},
$$
$a$ real, $a\ne0,$ has the value $-1$ for: