Find an Algebraic Expression Equivalent to the Given Expression $\sin ( \arctan u )$

Multiple Choice

Find an algebraic expression equivalent to the given expression.
- $\sin ( \arctan u )$

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