Find the mistake in the below maths equations

A = 2
A(A-1) = 2(A-1)
A2-A = 2A-2
A2-2A = A-2
A(A-2) = A-2
A = 1

Can you count the number of lines in the below picture?

Can you solve this amazing hard number series problem?
7, 8, 10, 12, 16, 18 ?

There was a kingdom in which the king had no heir to take over his thrown. Even the queen was dead and he himself was on the verge of dying. He thought about it and then summoned all of the teenagers. He gave one seed each to all of them and asked them to grow the plant. He announced that the one with the most beautiful plant will become the king/queen of the empire after the death of the king.

After a month, all of them were called. The king looked at all of the plants but announced the girl with an empty pot as the queen of the empire. Why?

What is the next number in this series?

4,12,84,3612....

Three fair coins are tossed in the air and they land with heads up. Can you calculate the chances that when they are tossed again, two coins will again land with heads up?

Count the Triangle in the figure given below:

You can hear me, but you can't touch or see me.

What am I?

Why do you find that most of the buildings are deprived of the 13th floor?

John was drowned by he was not wet. How?