Final answer:
To check your blind spot when changing lanes to the left, glance in the rearview mirror, over your left shoulder, and in the side mirror.
Step-by-step explanation:
When changing lanes to the left, you should check your blind spot by glancing in the rearview mirror, over your left shoulder, and in the side mirror. Checking all three areas helps ensure that you have a complete view of the road and any vehicles approaching from behind.