14. Let $x , y , z$ be positive numbers such that $x ^ { 2 } + y ^ { 2 } = z ^ { 2 }$. Determine the value of the following expression:
$$\frac { \log _ { y + z } x + \log _ { z - y } x } { \left( \log _ { y + z } x \right) \left( \log _ { z - y } x \right) }$$
(a) Undefined.\\
(b) $\frac { 1 } { 2 }$\\
(c) $\frac { 1 } { 4 }$\\
(d) 2\\