Lets take this one stat at a time.

30 **********in ability pow on the jaximus. That scales ****ing amazingly with all of jax's ability's, ofc makes sense.
30 attack damage. Every silver player knows that attack damage = win especially when it helps scale with the spellblade passive, AND jax's attack speed steroid, AND 85% of jax's abilitys, AND word.
30% Attack speed. Jax stacks his passives 30% faster = 100% beastin ***in awesome sauce
10% crit chance. With the runes that adds up to 11% crit chance. Think about the possibility's.
250 Heath scales well with Jax's ult making him all the moar tunky er.
200 mana gives you juuuuuuuuuuuuuuuuuuuust enough mana to not have any mana problems for the rest of the game
8% movement speed. wow. that's alot of walking pawar to keep up with your victims or to run away from an enemy rapist.
Rage passive. It seems a Little weak at first glance, but it gives you juuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuust enough movement speed extra to steadily shove your lamppost inside of the back of your opponents skull over and over again until they play the death animation of there character.
Spell Blade:
Unique Passive - Spellblade: After using an ability, your next basic attack deals 200% base AD bonus physical damage. (2 second cooldown).
Isnt that the most obviously OP and broken ability that you can have on a character with such low cool downs (at max ranks) like Jax? This is the main reason Tri force is so good on jax. He's tanky, deals lots of sustained damage, looks cool, and now he has **** tons of burst with this spell blade ********.

ofc there's more items than the ****ing tri force ya dim wit.
you need booties, a jungle items, a extra damage item, 2 tank items on my average jax build aswell!

Booties:
Buy merc treads if they have even just SOME cc. Crowd control is everything's counter, you should almost always get merc treads. Unless they have 5 champs without CC who is also all AD, like 5 Master Yi noobs.

Jungle items:
Usually get Elder Lizard because it gives so much early damage, its just much better than the mediocre 350 heath.

That one other damage item:
90% of jax playas will take the Blade of the Ruined King or even rush it, and for good reason. The stats that one item gives is so nice for slot efficiency, which is what you need when you get really fed and run outa space. But really, the BORK is really good on a AA reliant champ like Jax. But there's more items than just BORK :/ but really any item with life steal and some AD or AP will be perfect, that's all that's missing from jax at this point: moar lifesteal!

Them Tunk items:
Being tanky is really important on jax. Not only does it make it really annoying that the one dealing tons of damage, carrying your team, is also stupid tanky. But jax is one of those champ that need to be up in your face, and at melee range, to **** up his target, and he needs to tanky to survive the 1v5. One armor and one magic resist item of any kind will work on jax, even frozen heart.

Not much to talk about here.

The flat magic resist and armor is pretty standard for a bruisery type champ.
That one movement speed quint doe. Its better than putting flat damage or a life steal quint because it keeps juuuuuuuuuuuuuuuuuuuuust a little bit faster than an enemy without that little bit of movement speed, which can be life or death.

The life steal quints with the mastery adds up to 7% life steal at lvl 1. This makes you take no damage in the jungle tied in with your attack speed runes and steroids and the counter strike.

You might think im a ****in weirdo because these master are all over the place. But if anyone ever told you to take the average 21/9/0 route, **** them. Be a lonely kid by himself at recess like me and be a little diffrent.

I take 15 in offense with points in both AD AND AP because AP is underrated as **** on jax, also that spell weaving and blade weaving percent damage synergies well with jax's kit.

2 points in that enchanted armor **** for some tanky scaling

The 13 in utility really helps jax a lot. Jax is like lee sin with that ward mastery, ward hopin and ****. the runic affinity helps with keeping your buffs longer and the lifesteal/spell vamp is just the most op ***in **** on jax. the 40 starting gold helps with getting a extra ward because you dont need any heath pots when you have all that pimpin life steal.