Id take a guess and say line 1 because the rest looks correct
Answer:

Step-by-step explanation:
Given a circle centre J
Let the radius of the circle =r
LK is tangent to circle J at point K
From the diagram attached
Theorem: The angle between a tangent and a radius is 90 degrees.
By the theorem above, Triangle JLK forms a right triangle with LJ as the hypotenuse.
Using Pythagoras Theorem:

The length of the radius, 
AFB, the sides are similar
Next time please indicate which problem you want to work on.
One example of an equation with variables present on both sides is
y-b = m(x-a). Given the slope of a line and one point (a,b) through which the line passes, you can come up with an equation of the line.
Or, given the numeric value of y-b and that of x-a, you could obtain the slope of the line thru the points (x,y) and (a,b).