Weird Maths 'N Physics Teacher

 "If a=b and b=c then a=c, now give me the practical example of this principle from real life."Jack, "I love you sir and you love your daughter which means I love your daughter."

Teacher, "Dear Jack, right. Now I don't have a daughter, so in mathematics:
my daughter=0;
so your love=0;
so for you, if you are my student, you love me then I love you (newton's third law, every action has its reaction equal in magnitude but opposit to direction),
and you love your sister, which I know you have.
Hence it is proved that:
I love your sister; alternatively, your sister loves me (newton's third law)."