Write the Following as an Algebraic Expression in U, U $\sin ( \arctan u )$

Multiple Choice

Write the following as an algebraic expression in u, u > 0.
- $\sin ( \arctan u )$

A) $\frac { \mathrm { u } \sqrt { \mathrm { u } ^ { 2 } + 1 } } { \mathrm { u } ^ { 2 } + 1 }$
B) $\frac { \sqrt { u ^ { 2 } + 1 } } { u ^ { 2 } + 1 }$
C) $u \sqrt { \mathrm { u } ^ { 2 } + 1 }$
D) $\frac { \mathrm { u } \sqrt { \mathrm { u } ^ { 2 } - 1 } } { \mathrm { u } ^ { 2 } - 1 }$