First year Math help (1 Viewer)

[melimoo]

thanks a bunch guys!!

 

[xuvu6520]

You have to do the cross product first because if you did the dot product first, you'll be crossing a scalar with a vector, which doesn't work.

ooopse!!!

heheheh.

btw. I dunno whose account is this. This guy was logged in from Mathematics Library.

 

[LostAuzzie]

I'm stuck with question 4d.
Find the equation of the line that lies in plane p passes through point C and is perpendicular to the line l
I tried using the fact that the line is perpendicular to l and the normal to p, but that ended up giving me a plane
Anyone got any ideas, no answers just an idea of how to approach it
Any help would be much appreciated

 

[melimoo]

I'm stuck with question 4d.
Find the equation of the line that lies in plane p passes through point C and is perpendicular to the line l
I tried using the fact that the line is perpendicular to l and the normal to p, but that ended up giving me a plane
Anyone got any ideas, no answers just an idea of how to approach it
Any help would be much appreciated

i forget if i could do that one. i'll get back to you tomorrow after my notes have dried. yes, i did spill a whole full glass of water on all my math1002notes. fuck

 

[LoneShadow]

I'm stuck with question 4d.

Post a copy of the assignment. Maths website is down or something. Or it's just me.

 

[LostAuzzie]

Yer it was down last night, should be up now though, if not heres the assignment

 

[KeypadSDM]

It's the line in the plane P which is perpendicular to the projection of l onto P. Just work out the projection of l onto P, and then cross product its direction with the normal of P to find the direction of your required line.

Given the intersection coordinates you can find the equation of the line (i.e. you have the gradient (direction) and a point on the line)

 

[acmilan]

Is that assignment worth more than 5%? Last year we had like 2, 3 questions tops in an assignment.

 

[LostAuzzie]

It's the line in the plane P which is perpendicular to the projection of l onto P. Just work out the projection of l onto P, and then cross product its direction with the normal of P to find the direction of your required line.

Given the intersection coordinates you can find the equation of the line (i.e. you have the gradient (direction) and a point on the line)

Thankyou for that, very much appreciated

And acmilan, only 2 of the questions are marked

 

[melimoo]

ok here are my issues:

1c) find a unit vector perpecndicular to a and b+c
now i can find one perp. to a, but how do i find one perp to both?

2b) i figure i have to use the result from part a), and then use pythag. or sometihing...but how & where & why does a . b come into it?
2c) maybe would make more sense if i had b)??

also 4c) and d)
they make me cry.

any help is welcomed help and possibly repaid in sexual favours.

 

[heart]

for 1c) it's just a x (b+c)... and then make the result into a unit vector

2b) Just say |AP|²= AP.AP and then a.b will come in the answer and do the same for |CP|²

c) this does make more sense if you do 2b

And i don't think i did 4c properly =P

 

[LostAuzzie]

For Question two you use the Cosine Rule and end up with, a^2, B^2 & a.b all in the one equation

 

[Libbster]

um yeah, i really should go and start the assignment. lol

 

[AntiHyper]

The markers for this assignment must be pretty lazy lol

You should complete all questions, but only two will be marked

i hope they picked the questions i'm doing well.

 

[melimoo]

okay. how i love this thread
this is a last resort cause ive tried and really can't do any of the following from the math1001 assignment:
3b
4c
5

http://www.maths.usyd.edu.au/u/UG/JM/MATH1001/r/PDF/ass2.pdf

for 3b, i looked at how the limit behaves as you approach along x-axis, y-axis and the line x=y. and for all i got them to be = 0. essentially i was trying to show that the limit didn't exist, but to my understanding it doesn't exist if all those values aren't equal. so is the limit = 0? or does it exist? wah

4c, trying to sub in x = pi/2 and x= 3pi/2 and show that they are different signs. they both = 0
:/

5, no fucking idea

please help meeeeee thankyou <3

 

[SeDaTeD]

For 3 b, let it approach the origin along y=kx, for some constant k.

for 4c, use part a, which says the limit as x-> pi/2 is 1, and that f(x) is essentially the same as the equation except for one point and that it is continuous. Sub in 3pi/2 then use intermediate value theorem.

q5, by MVT, you have, for some c, a<c<b, -sin(c) = [cos(b)-cos(a)]/[b-a]. But |-sin(c)| =< 1 for any c. so |[cos(b)-cos(a)]/[b-a]| =< 1. Rearrange to get the result.

 

[melimoo]

thankyou. it helped...a little