Please send the solution to the problem given in the attachment.

see this . both are correct. you will get pi from these both of them

see in the last step correct there it is 2pi

if you have any doubt then ask

see these videos https://youtu.be/Da8-KYQ8CiI https://youtu.be/yXiDBFCyq6s https://youtu.be/au9xC5sxyDk https://youtu.be/GfRPD4xg1wc

see you can use this also

see this

according to me option c is correct