Forget all of the mathematical permutations, all the equations tougher than anything in “Good Will Hunting” or “A Beautiful Mind.” The Red Bulls’ task is simple, if not easy; win at rival Philadelphia on Saturday (1:30 pm, NBC) and they essentially will seal third place in the Eastern Conference and a playoff bye. If they don’t, they will be consigned to the capricious wild-card round next week.

“It’s very crucial,’’ said coach Hans Backe, whose job status has come under constant scrutiny, and appears to rest on winning the team’s first-ever MLS Cup. “It’s good to know the conditions, that we need to win to finish third. That means we have a full week to the next week. Otherwise we have to play a wild-card game on Wednesday. So it’s a massive game.”

The Red Bulls can clinch third with a win, coupled with any of the following: a Chicago loss against D.C. Saturday, a Chicago/D.C. tie (the Red Bulls must maintain their plus-nine scored advantage over the Fire), or a Chicago win (the Red Bulls must hold their plus-two goals scored advantage over United).

If they finish third, they will play host to the first leg of the Eastern semifinals either Nov. 3 or Nov. 4 with the return leg on the road either Nov. 7 or 8. But if they fail to win today at PPL Park, they will have to play the knockout round either Wednesday or Thursday.

brian.lewis@nypost.com