Could you please explain to me how to construct an iso-contribution line? I understood on your lecture, but when I was doing BPP revision kit questions 34, 35 and 36, I don’t understand how do they get these answers.
It is only the angle/gradient/slope of the iso-contribution line that is important, and the angle of it will be the same for any total contribution.
So you use any figure you want for the total contribution in order to draw the line. Depending what figure you choose, the line will be in a different place, but this is not relevant – the angle will always be the same and it is only the angle of the line that we are interested in.