Provide an Appropriate Response $\left\{ \mathrm { r } _ { \mathrm { n } } \right\}$

Multiple Choice

Provide an appropriate response.
-A sequence of rational numbers $\left\{ \mathrm { r } _ { \mathrm { n } } \right\}$ is defined $b \mathrm { y } \mathrm {} \mathrm { r } _ { 1 } = \frac { 2 } { 1 }$ , and if $\mathrm { r } _ { \mathrm { n } } = \frac { \mathrm { a } } { \mathrm { b } }$ then $\mathrm { r } _ { \mathrm { n } } + 1 = \frac { \mathrm { a } + \mathrm { b } } { \mathrm { a } - \mathrm { b } }$ . Find $\mathrm { r } _ { 50 }$ .

A) 3
B) 49
C) 50
D) 2