Final answer:
You are in a car's or truck's blind spot when you cannot see the driver's face in their side mirrors or rearview mirror. Checking the visibility of the vehicle's headlights in your mirrors can also help determine if you are in a blind spot. Always use your mirrors and turn signals to safely navigate around other vehicles.
Step-by-step explanation:
You know you're in a blind spot when the driver of the other vehicle cannot see you in their side mirrors or rearview mirror. When you drive alongside another car, especially a large truck, there may be areas along the sides and rear where you are not visible to the driver. One way to determine if you are in a blind spot is to look at the mirrors of the vehicle beside you. If you can't see their face, they can't see you. It is always important to be aware of blind spots, adjust your position, and use your turn signals before changing lanes to communicate your actions to other drivers.
To test this, you can position your car at different angles and distances from a parked vehicle with its headlights on. As you move, observe when the headlights disappear from your view and when they become visible in your mirrors, indicating that you've entered or left the blind spot. Remember, never directly look at bright lights to avoid damaging your eyes.