Verify That the Equation Is an Identity $$\sec ^ { 2 } \frac { u } { 2 } = \frac { 2 \sec u } { \sec u + 1 }$$

Essay

Verify that the equation is an identity.
- $$\sec ^ { 2 } \frac { u } { 2 } = \frac { 2 \sec u } { \sec u + 1 }$$