Some doubts in 2's complement I am doing one question in which we have to find 2's complement of 43. I know to find 2's complement we have to find 1's complement and then add 1 into it to get 2's complement.

So here is how I am doing it -

Binary value of 43 is 00101011. (We have to use 8-bits to represent)

1's complement is 11010100. 

2's complement is 11010101.

But the original answer is 00101011.

I used some online converter and they are giving same answer as the original one. But i don't find any mistake in my method. So please help me to understand my mistake and how to get the original answer.

Edit -

This is the link to online converter : Click Here.

Update -

As said by one user that my question is wrong or it is wrong in textbook. It is not. Same wording of question above in my question. Here's the link from which I am solving this question before. 

Click here to see.

And I wrote answer later from this link. As you can see in my answer below.
You were correct and the textbook is still wrong. Not surprising given what a slapdash job they did of putting it together. I'm quoting from the second page you linked:

Explanation: In$2$’s complement representation, positive numbers are represented as their representation and negative numbers are represented by first doing $1$’s complement, then adding $1$ to the result.

Notice the lack of a space between &quot;in&quot; and &quot;$2$’s&quot;? Just that little detail gives me serious doubts as to whether they even know what the hell they're talking about.
Well, to be fair, they do know what they're talking about, they just don't know how to explain it simply and correctly. &quot;Represented as their representation&quot;? What does that even mean? &quot;And negative numbers are represented by first doing $1$’s complement&quot; on what? On their absolute value or on some random number?

So $43$ is represented as $00101011$.
Note that option represents $-43$.

Are they saying that $00101011$ represents both $43$ and $-43$? Maybe they meant to write something else between those two sentences but just didn't get around to it.
The answer is indeed $11010101$ like you got, which means $-43$ in a signed $8$-bit representation using two's complement, or $213$ in an unsigned $8$-bit representation. If they wanted $00101011$, they should have asked for the the $8$-bit representation of $43$.
And lastly, what sort of material are you supposed to read and understand before taking the quiz? Here's an explanation of two's complement from Cornell University: https://www.cs.cornell.edu/~tomf/notes/cps104/twoscomp.html
Although the author of those Cornell notes says the topic doesn't need a lengthy explanation, I think you will find his explanation far more detailed, correct and easy to undestand than anything on GeeksForGeeks.org.
And if after reading that you still have &quot;doubts,&quot; try the following exercises with pencil on paper:

$00000101 + 00000011$
$11010101 + 00000011$
$11011000 - 00000011$
$11010101 \times 11111111$
Your answer is correct. In two's-complement representation, positive numbers are simply represented as themselves, and negative numbers are represented by the two's complement of their absolute value. 

Here's Wikipedia explanation you can see.