Answer
The identity is verified.
$(sin~x+cos~x)^2=1+sin~2x$
Work Step by Step
Use: $cos^2x+sin^2x=1$ and $sin~2x=2~sin~x~cos~x$
Start on the left side:
$(sin~x+cos~x)^2=sin^2x+2~sin~x~cos~x+cos^2x=(sin^2x+cos^2x)+2~sin~x~cos~x=1+sin~2x$