Solve $\left\{ \begin{array} { l } x ^ { 2 } + y ^ { 2 } = 36 \\x ^ { 2 } - y ^ { 2 } = 36\end{array} \right.$

Multiple Choice

Solve: $\left\{ \begin{array} { l } x ^ { 2 } + y ^ { 2 } = 36 \\x ^ { 2 } - y ^ { 2 } = 36\end{array} \right.$

A) $\{ ( 6,0 ) \}$
B) $\{ ( 36,0 ) \}$
C) $\{ ( 6,0 ) , ( - 6,0 ) \} \}$
D) $\{ ( 0,6 ) , ( 0 , - 6 ) \}$