

Slope of the two non vertical lines is
.
Replace
in slope formula.

(Subtract:
)
Apply multiplication property of equality: Multiply each side by k
2.
(Cancel common terms)
Apply division property of equality: Divide each side by negative 2.
\
(Cancel common terms)
Apply addition property of equality: a=b then a+c = b+c.
\
(Add 2 to each side)
(Add:
)
Check:
\To check the solution, substitute
in original equation.

(Subtract:
)
(Cancel common terms)
Compare the values, the equation is true.
The value of
.