Impulse reponse from step response

[jaus tail]

Homework Statement

Homework Equations

Derivative of step response is impulse response

The Attempt at a Solution

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I marked A cause it matches the other coefficients. But where does 9 come from in the last term.
I tried with laplace and got the last term as 9. But how to get that in time domain with differentiation?

 

[scottdave]

Do you need to use the product rule when you differentiate these functions? I am not sure if you do - because it's been a long time since I've done these step and impulse response problems.

 

[scottdave]

I would think that the product rule still applies here.

 

[jaus tail]

Oh yes. I get the right answer if I use the product rule. In solved examples there wasn't any u(t) or δ(t).
Thanks.

 

[jaus tail]

Can you please help me with the below question?
https://www.physicsforums.com/threa...t-right-answer-but-not-matching-graph.939189/
I have an exam tomorrow.