[tex]\qquad\qquad\huge\underline{{\sf Answer}}[/tex]
Let's use distance formula ~
[tex]\qquad \tt \dashrightarrow \:LJ = \sqrt{(x1 - x1) {}^{2} + (y2 - y1) {}^{2} } [/tex]
[tex]\qquad \tt \dashrightarrow \:LJ = \sqrt{(0) {}^{2} + (y2 - y1) {}^{2} } [/tex]
[tex]\qquad \tt \dashrightarrow \:LJ = \sqrt{ {}^{}(y2 - y1) {}^{2} } [/tex]
[tex]\qquad \tt \dashrightarrow \:LJ = { {}^{}y2 - y1 {}^{} } [/tex]
I hope it was easy enough to understand, ask me if you have any doubts ~
