C3 Trig question

The lines l1 and l2, with equations y=2x and 3y=x−1 respectively, are drawn on the same set of axes. Given that the scales are the same on both axes and that the angles that l1 and l2 make with the positive x-axis are A and B respectively,

(a) write down the value of tan A and the value of tan B;

(b) without using your calculator, work out the acute angle between l1 and l2.

I've got part a) but I'm confused about part b). The answer says we must find tan(A-B) but I can't really seem to visualise why that's the case. Could someone explain why we find tan(A-B) please?

A-B is the angle between the lines. If you know tan(A) and tan(B), just use the formula for tan(A-B) = (tan(A)-tan(B))/(1+tan(A)tan(B)). Hopefully, its a well known value.

Tbh I can't really see why A-B is the angle between the lines.

Have you sketched the lines and marked A & B on there? It should be obvious?

Tbh I can't really see why A-B is the angle between the lines. Oh, it might be because I drew B below the x-axis. If you draw it above the X-axis, it becomes clear why the angle is A-B

A-B is the angle between the lines. If you know tan(A) and tan(B), just use the formula for tan(A-B) = (tan(A)-tan(B))/(1+tan(A)tan(B)). Hopefully, its a well known value.

how did you get part a