How does this mark scheme work A Level maths

https://imgur.com/a/GRWBAxu

Could anyone help me decipher what this edexcel maths mark scheme actually means? I'm doing this exam question, for part b I didn't write out the part that says "dM1".
Apparently this means dependent? I'm guessing that just means it's dependent on you getting M1 beforehand but not sure.

If I answered like this in an exam would I get all the marks? I tend to skip writing that out usually