Answer :
when you have a warm shower, you create steam. So when the warm steam flows in the air and starts to be in contact with a cold surface, it condenses causing a mist to form on the cold surface. The heated mirror is warm so, when, the steam is in contact with the mirror condensation is prevented. Therefore, the mirror stays clear.
Cause the only reason a mirror becomes misty when you take a shower is because the steam from the water rises and then condenses on the cold surface of the mirror cause it cools down the steam back to it's origional form of water. But if you had a heated mirror the steam wouldn't condense back to water when it touched the mirror so the mirror stays clear:)
