Math thread! Come in and have some pi...

[Muckle_Ewe]

Let a,b,c be vertices of a right triangle with c = 90 degrees. If p is a point on |AC| and AP =6, BP bisects CBA, and BPC = 60 degrees, what is |BC|?

I got 4*sqrt3/3 it's not in the choices. WTF

I fawking HATE geometry and I'm sh*t at it but this is how I think it's done...

EDIT: My drawing should say |BC| = 3sqrt(3)



Notice the key word being bisect here...

Also, did I say I'm sh*t at geometry. This might be wrong.

[MiKey4]

Hey I do research involving optics so I'm always having to sit down for 5 hour sessions figuring out the geometry of some new lens design or something like this, then sometimes it's involving harmonics, etc, maths is awesome and I think anyone who disagrees must have had a bad teacher some time in their childhood.

just sayin hi

[Jaycee41]

could use mathematical induction to prove equality between the two statements in order to prove symmetry but I imagine induction is a bit complex for a 16 year old math class


Assuming they are equal (which you normally can in whatever level of math you are in) symmetric functions dictate equality for all real numbers.

That choice is actually on there. Finally :O and Marc i understand mathematical induction clearly.

[Jaycee41]

Two cases... (sqrt(x) = x^(1/2) by the way, I just think it looks neater here)

Right hand side is always non-negative so |x| >= sqrt(2)

So first case, x >= sqrt(2)

x^2 - 2 = 4x + 2

x = 2 + 2sqrt(2) or 2 - 2sqrt(2) but!

|2 - 2sqrt(2)| is less than sqrt(2) so we rule that one out and get one root as 2 + 2sqrt(2)

Next case x <= -sqrt(2)

x^2 - 2 = -2(2x + 1)

=> x = 0 or -4 but then 0 is not less than -sqrt(2) so -4 is our other root.

Hence sum is -4 + (2 + 2sqrt(2)) = 2sqrt(2) - 2

But u don't get sqrt2 for it being above y=0. it's actually 1/2.

[Muckle_Ewe]

But u don't get sqrt2 for it being above y=0. it's actually 1/2.

What? Not really sure what you mean. Right hand side has to be equal or greater than zero yes? Hence so must left hand side. Hence x^2 must be greater than or equal to 2 which means x must be greater than or equal to sqrt(2).

[Jaycee41]

What? Not really sure what you mean. Right hand side has to be equal or greater than zero yes? Hence so must left hand side. Hence x^2 must be greater than or equal to 2 which means x must be greater than or equal to sqrt(2).

Solving the abs value inequality 2x+1 gives u 1/2, not Sqrt2.

[Muckle_Ewe]

Solving the abs value inequality 2x+1 gives u 1/2, not Sqrt2.

No.


The right hand side will be positive for ALL x values.

But, I can see what you're getting at.

Let's say that the right hand side would be positive for all x values above 1/2 ok. This is NOT the case here but let's pretend it is.

Now we know that x must be greater than 1/2

BUT

The left hand side tells us x must be greater than sqrt(2).

So...

What would happen if x is greater than 1/2 but less than sqrt(2)?

The right hand side would be positive and the left hand side negative.

So we need to have x greater than sqrt(2)!

You may be misunderstanding the absolute value symbol.

|x| = x is x is positive, -x if x is negative.

Hence, |x| can never be negative.

[Jaycee41]

No.


The right hand side will be positive for ALL x values.

But, I can see what you're getting at.

Let's say that the right hand side would be positive for all x values above 1/2 ok. This is NOT the case here but let's pretend it is.

Now we know that x must be greater than 1/2

BUT

The left hand side tells us x must be greater than sqrt(2).

So...

What would happen if x is greater than 1/2 but less than sqrt(2)?

The right hand side would be positive and the left hand side negative.

So we need to have x greater than sqrt(2)!

You may be misunderstanding the absolute value symbol.

|x| = x is x is positive, -x if x is negative.

Hence, |x| can never be negative.

Interesting. I didn't know this.

[charity4thepoor]

feels good brahs

[MUFC]

Guys, what can I do with my BSc in Applied Math? My grades will not be good enough to get into grad school. Other than Actuarial work, i'm lost. Halp?

Actually, meh. I still have 4 full semesters left in order to graduate, and my GPA is a 2.00. Could significantly improve.

[FatWhiteKid]

3 + 50 = 350?

[Jaycee41]

Guys, what can I do with my BSc in Applied Math? My grades will not be good enough to get into grad school. Other than Actuarial work, i'm lost. Halp?

Actually, meh. I still have 4 full semesters left in order to graduate, and my GPA is a 2.00. Could significantly improve.

Wth? How did you end up with a 2.0...

Brb doing math to find out you got at LEAST 5 F's or 8 D's or 11 C's.

[MUFC]

Wth? How did you end up with a 2.0...

Brb doing math to find out you got at LEAST 5 F's or 8 D's or 11 C's.

I bounced around majors my first 3 semesters. Most of my grades in math courses are at least Bs.

[MUFC]

Spend one more semester, or 2 summers retaking some F's and D's. Imagine just adding a 4 or 3 to your quality point sum for each class you take. It will jump quickly.

Yea, that is what I'm thinking. When I graduate, it's just after the fall semester (so, in 2 years). I should spend the next semester in school retaking some classes.

[Stteven]

Question:

Trigonometric Identities

(1-sin^2x)(1+tan^2x)=1
(cos^2x)(1+tan^2x)=1
(cos^2x)(sec^2x)=1
Possible step...?
(cos^2x)(1/cosx)=1

Unsure how to finish this... measly reps for answer.

[karinyoso]

sup math brahs. anybody know a good reference differential equations text book? Most of my engineering classes this term are getting more into DEs/Laplace/Vector Calculus and I've forgotten most of those stuff

[Muckle_Ewe]

So maths chaps what courses you taking this year and how's it all goin?

Currently doing my masters and this semester is...

Fluid dynamics
Scientific computing
Computational stats
Extrasolarplanets and astrophysical discs.

Sounds like in doing physics lol but I don't really enjoy pure math so stick with all the applied stuff.

Final project will be on finding analytical solutions to orbits near Lagrange points.

[oldmilwaukeee]

Got a really simple problem i cant figure out

f(x)=ax^3+bx^2+cx+d
find a,b,c,d if f(x) has a inflection point at 0,2 and a local max at 2,6

[batman15]

Ask a guy taking "beginning and intermediate algebra" anything.

[Greg1983]

Got a really simple problem i cant figure out

f(x)=ax^3+bx^2+cx+d
find a,b,c,d if f(x) has a inflection point at 0,2 and a local max at 2,6

Well you know f''(0) = 0 (second derivative at inflection point) and f'(2) = 0 (first derivative at local max/min). So:

f'(x) = 3ax^2 + 2bx + c
f''(x) = 6ax + 2b

f''(0) = 0 => b = 0
f'(2) = 0 => 12a + c = 0

Putting these in the original function:

f(x) = ax^3 - 12ax + d

Now you also know f(0) = 2 and f(2) = 6.

f(0) = d = 2
f(2) = 8a - 24a + d = 8a - 24a + 2 = -16a + 2 = 6 => a = -0.25
From above 12a+c = 0 => c = 3

So:
a = -0.25
b = 0
c = 3
d = 2

Assuming I didn't make an arithmetic mistake (which happens far too often) that'll do it.

[Boatski]

Well you know f''(0) = 0 (second derivative at inflection point) and f'(2) = 0 (first derivative at local max/min). So:

f'(x) = 3ax^2 + 2bx + c
f''(x) = 6ax + 2b

f''(0) = 0 => b = 0
f'(2) = 0 => 12a + c = 0

Putting these in the original function:

f(x) = ax^3 - 12ax + d

Now you also know f(0) = 2 and f(2) = 6.

f(0) = d = 2
f(2) = 8a - 24a + d = 8a - 24a + 2 = -16a + 2 = 6 => a = -0.25
From above 12a+c = 0 => c = 3

So:
a = -0.25
b = 0
c = 3
d = 2

Assuming I didn't make an arithmetic mistake (which happens far too often) that'll do it.

Had calc 1 last semester and already forgot that, fml.

[Muckle_Ewe]

Ask a guy taking "beginning and intermediate algebra" anything.

Have you prepared your anus?

(I dunno what those courses involve but if it goes onto group theory... anus pain will come...)

[charity4thepoor]

Have you prepared your anus?

(I dunno what those courses involve but if it goes onto group theory... anus pain will come...)

pretty sure its like pre college algebra lol



im in abstract algebra I and complex analysis right now. like the abstract so far.

[marcFE]

Do the few of you who follow this thread that have taken the GRE in math have any good tips you wish you heard before taking the test? Been studying my ass off for the last few weeks and the only thing I have concluded is that time is definitely relevant since some problems can take quite a while.

[stanlee010178]

Do the few of you who follow this thread that have taken the GRE in math have any good tips you wish you heard before taking the test? Been studying my ass off for the last few weeks and the only thing I have concluded is that time is definitely relevant since some problems can take quite a while.

Just keep practicing. The problems aren't hard, its just recognizing what the problem is asking, then elimination from there.

[Muckle_Ewe]

http://web.mit.edu/abhinavk/www/inte...e/qual2011.pdf

For any integral fans out there...

[NeoKantian]

Do the few of you who follow this thread that have taken the GRE in math have any good tips you wish you heard before taking the test? Been studying my ass off for the last few weeks and the only thing I have concluded is that time is definitely relevant since some problems can take quite a while.

Did you have classes in all the material it covers?

[marcFE]

Did you have classes in all the material it covers?

Most of it, as dumb as it sounds the pre-calc/trig concepts are the things raping me since relearning all the trig properties is rather tedious. Have not taken abstract algebra or number theory so have been trying to teach it to myself but the practice tests I have taken have only had 2-3 questions from those fields so may just end up skipping them unless they are something I can solve with my weak knowledge in those fields.

[MiscMathematician]

Have you prepared your anus?

(I dunno what those courses involve but if it goes onto group theory... anus pain will come...)

A friend of mine just graduated with her PhD, she's from Europe. She's now a professor here in the US and was asked to teach college algebra. She was happy until she figured out that it isn't what she knows as algebra lulz

[Muckle_Ewe]

lol. That looks like a bitch of a time constraint.

I know 20 minutes for 25 of them! You don't even have time to stop and think... I've not had to do any half difficult integral in a while so think I'll use that test for a bit of practice. Will definitely go over the 25 min limit though...