How find an angle between two lines

Hi gays, I’m realy noob and need you help!
How can i find angle between to lines
PS sorry about my English

If line 1 goes through points (ax1,ay1) and (ax2,ay2), make.
m1=(ay2-ay1)/(ax2-ax1) --slope of line.

Do the same for line 2 to calculate m2

Then the angle A between them is calculated from

tan(A) = abs((m1-m2)/(1+m1*m2))

Or you could define the two vectors along the lines and use the inbuilt angleBetween method. Using Ignatz’ notation:

u = vec2(ax2-ax1,ay2-ay1)
v = vec2(bx2-bx1,by2-by1)
a = u:angleBetween(v)

Or all in one:

a = vec2(ax2-ax1,ay2-ay1):angleBetween(vec2(bx2-bx1,by2-by1))

(Look up the documentation to see whether the result is in radians or degrees.)