PJK and QKJ are right angles. We can make the right angled PQR, where QR is parralel to our JK (and congruent, true).
PR is PJ-QK=11-3=8. We've got PQ=17 and PR=8. Pythagoras' theorem could help us find out QR, which is equal to JK. [tex]QR=\sqrt{17^2-8^2}=\sqrt{289-64}=\sqrt{225}=15[/tex]
JK is that same 15, for the same reasoning.
