Author Topic: math hw...need help (Read 7903 times)

dinhotheone · « **on:** September 13, 2007, 02:33:00 pm »

i was doing my AP physics hw and i ran across a problem where you have to do projectile motion and figure out two angles whoch you can shoot water out of a hose and still get it in a bucket. it seemed not to hard until i simplified it to this:

sin(-54125+)cos(-54125+) = .21
(-54125+) = theta btw

to clarify: sin(theta)*cos(theta) = .21

now i know how to do this on the calc but i was wondering if anyone knew how i would go about getting the answer analytically.using inverses just seems like a bad idea and this is the one problem that has stumped me tonight/ this year so far. any math wiz's would be nice if they could help. usually i am good at math but i cant seem to figure this out. hmm i wonder if mathematica could help....anyway any help would be appreciated.

edit: no on that about mathematica

Ranman · « **Reply #1 on:** September 13, 2007, 02:54:00 pm »

Would Soh Cah Toa help?

bfr · « **Reply #2 on:** September 13, 2007, 03:13:00 pm »

*bfr tries to remember trig

"sin(theta)*cos(theta) = .21" Can be turned into:

sin(2*theta)/2=.21
sin(2*theta)=.42

If that helps.

"using inverses just seems like a bad idea" From what I remember, inverses should probably work though.

Ranman · « **Reply #3 on:** September 13, 2007, 03:15:00 pm »

Or what about this:

Product to Sum Identities:
$user posted image$

Courtesy of Wikipedia:
http://en.wikipedia.org/wiki/Trigonometry

Edit: bfr beat me to it.

dinhotheone · « **Reply #4 on:** September 14, 2007, 05:02:00 am »

thanks guys but you 2 were beaten to it by my little brother. on the way to school this morning i told him about it and he figured it out right away, apparently he just did those precalc thoerems the day before or something. i totally forgot em.

@bfr, i meant inverses at the point where i was not once you have it simplified into a single trig function.

thanks for your help guys

simplethinker · « **Reply #5 on:** September 14, 2007, 05:40:00 am »

sin(x)cos(x)=.5sin(2x), not 2sin(2x)

For determining the angle you need, just do .5arcsin(g*x/v^2)

DJ Omnimaga · « **Reply #6 on:** September 14, 2007, 09:01:00 am »

Hey welcome member #... uhm 2193?

? O_O

ok I didn't realised that many spambots tried to register before you, there is only 301 members accounts currently on the forums

welcome anyway simplethinker

simplethinker · « **Reply #7 on:** September 14, 2007, 09:53:00 am »

Thx

I've been on UTI for a couple years but just created accounts for here and ti-freakware

DJ Omnimaga · « **Reply #8 on:** September 14, 2007, 10:00:00 am »

cool i hope you like the forums and especially the programs

Delnar_Ersike · « **Reply #9 on:** September 14, 2007, 01:26:00 pm »

Don't forget the Introduce Yourself topic, as I can't officially give you some peanuts unless you post there.

Liazon · « **Reply #10 on:** September 14, 2007, 01:52:00 pm »

QuoteBegin-bfr+13 Sep, 2007, 21:13-->

QUOTE (bfr @ 13 Sep, 2007, 21:13)

*bfr tries to remember trig

"sin(theta)*cos(theta) = .21" Can be turned into:

sin(2*theta)/2=.21
sin(2*theta)=.42

If that helps.

"using inverses just seems like a bad idea" From what I remember, inverses should probably work though.

ya, that's what we used in out physics class to make life so much easier. duno why they don't just show you that too, but i guess they just want you to figure it out.

are you planning to take the B or C tests?

simplethinker · « **Reply #11 on:** September 14, 2007, 02:38:00 pm »

Heres a tip on how to get the most out of AP Physics:
switch teachers until their syllabus doesn't say "AP test" more than "physics"-it works, trust me

tifreak · « **Reply #12 on:** September 14, 2007, 11:29:00 pm »

Another site that should be brought to people's attention is http://www.freemathhelp.com/forum/index.php since it is a site about that kind of help.

dinhotheone · « **Reply #13 on:** September 15, 2007, 04:22:00 pm »

no, i think i went at the problem a different way and thats why i ran into the problem its not like the teacher knew where i would go with the problem. you see, it may seem odd coming from someone who just asked for help on a problem, but i''m genereally the one doing the explaining in my class, not the teacher.

@liazon
i already have 2 other ap's (bio, stats) and im probable gona take the bc calc test as an independant study so i wouldnt have room for more ap's even if i wanted to (my school only has 4 slots)

simplethinker · « **Reply #14 on:** September 16, 2007, 07:22:00 am »

Are you going to take the BC Calc test later in the year? Don't trust the on-line sample exams, get a study guide from your school. I tried over the summer, but had nothing from the online test. Good sites are: calculus.org, and the wolfram mathematica. You have my same schedule, AP Stats, AP Physics, AP Stats, AP Bio.
The things I missed on the BC test were: the epsilon-delta proofs, differentiation of 2D parametrics (not with vectors), the exact names, uses, and derivation of the series convegence/divergence theorems. Even though they're not on the online exams, you will need them.

Author Topic: math hw...need help (Read 7903 times)

Delnar_Ersike

Liazon