Year 10 circles. How to determine when to use when?

[ivory cloud]

I mean, it’s quite self-explanatory-

It’s showing you scenarios

[spare heath]

But like

[spare heath]

They kinda look the same?

Like the first part 2nd formula and the 2nd part 1st formula

[ivory cloud]

[spare heath]

[ivory cloud]

these two??

[spare heath]

Like

[ivory cloud]

1 is for the lengths of segments, the other is related to angles

[ivory cloud]

similarly for this

[spare heath]

Ohhh