Question

In the Boolean algebra, of the following one which is not equal to $A$ is

• A. $A.A$
• B. $A+A$
• C. $\overline{A}.A$
• D. $\overline{\overline{A}+\overline{A}}$

Answer 1

Answer: (C)

$\overline{A}.A$

The truth table for AND gate is given as shown in the figure.
When $A$ is true, $\overline{A}$ is false and vice versa.

Hence value of $\overline{A}.A$ is always false(looking at the second and third row of the table) which is not equal to $A$.

Hence, option C is the answer.