And just a tip (because I often see my friends in Stats doing a lot more work than they need to): it's really a mode setting (and TI finally put it in the MODE menu in the MP OSes, as chattahippie said), so if you don't have an MP OS and you're finding the DiagnosticOn token in the catalog (like Builderboy said), you only need to do so once and the r-values will stick around unless you clear your RAM.

And like Builderboy, I have absolutely no idea why TI doesn't just show them by default—they're so commonly used and don't take very long to calculate (at least from what I've seen), and when you're using LinReg they just fill two rows on the screen that would have been empty anyway, so there's no disadvantage there...

You could also use nDeriv( to find slope of the tangent line. The syntax is nDeriv(<expression>,<real>,<number>), where <expression> is the original curve (which you used for Tangent(), <real> is the independent variable (here X), and <number> is the X-value of the tangent. So if you wanted to find the tangent equation of Y=X² at X=3, the slope would be

nDeriv(X2,X,3)

For your second question, here is a nice guide. Basically, since you know the slopes, you can find the tangents of the two angles, and since you can find the tangents of the two angles, you can find the actual angle difference.

Can anyone tell me how to use the StartTMR function pls?

You can also do startTmr-A which does the same as checkTmr(A). Prolly less optimal though.

TI-BASIC only allows single-letter variable names, but list names can be up to five characters long.

hey i recommend not to program in TI-BASIC and to program in axe
it's much more convenient
and faster too

I code in Axe but I don't agree with your argumentation because in the same lines, one could say "hey I recommend not to program on a calculator and to program on a PC. It's much more convenient and faster too".

But what about people who like challenges ? Coding awesome things on a limited platform ? Coding awesome things on a limited platform in its most limited language ?
And what about people who have friends who don't know at all how to run ASM programs so they "have to" program in Basic if they want their friends to play their games (and don't tell me "introduce them a shell" because I tried and they told me a month later "how do I quit MirageOS ? I never used it in a month and I don't remember". And don't tell me "introduce them DoorsCS" because they had regular 83+ calculators. And don't even speak about zStart, they don't know what a RAM Clear is) ?

(Also, Axe is not always "much more convenient". Try to make an advanced maths program. I don't say you wouldn't manage, just that you would have got the same result in half no time in Basic).

hey i recommend not to program in TI-BASIC and to program in axe
it's much more convenient
and faster too

Although Axe makes graphics and animations much easier to display, it's much harder for other things, though. It took me hours just to implement switching between levels in Super Sonic Ball and about a day to make a Tunnel game (something I did in a few hours in xLIB 84C despite not being designed for side scrolling games). Besides, it's against Omnimaga rules to discourage people from using a language or another, especially in an help topic about a specific language.

it's against Omnimaga rules to discourage people from using a language or another, especially in an help topic about a specific language.

i'm sorry. i won't ever do that again. EVER. I PROMISE.
but yeah axe can also be difficult to code sometimes, i agree