Sir in exercise 7.4 solution instead of Perimeter it says Parameter?

Hi Panagiotis!

Thanks for reaching out.

Please accept my apologies for the delayed response.

Regarding the lecture you are referring to (as seen in the question), there is no mentioning neither of a parameter, nor of a perimeter. 

Otherwise, there is an exercise on measuring a figure's perimeter, so please just make sure if you are doing that one or another exercise. Thank you.

Hope this helps.
Best,
Martin