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#2 Help Me ! » Complex Numbers » 2007-05-23 00:12:09

renjer
Replies: 4

cos (2z) = 1 + i
where z = x + yi
Find all solutions for z.

I really can't solve this, pls help.

#3 Help Me ! » Singular Perturbations » 2007-03-23 02:06:21

renjer
Replies: 0

Ey"+(3+x)y'+xy=0, 0<x<1, 0<E<<1, subject to y(0)=20, y(1)=64. Find a leading approximation to the inner and outer solutions and match them.

However, I can't seem to match the two solutions, because when E tends to 0 in the inner solution, the inner solution tends to 20. While, my outer solution tends to 27e as E tends to 0.

I stretched x=Ex, and since the boundary layer is near x=0, i used y(1)=64 for the outer solution, and y(0)=20 for the inner.

Please help if anyone knows about this.

#4 Re: Help Me ! » Pls expand this for me » 2007-03-09 02:50:51

No, its not. We have to somehow expand that and compare it to another equation.

#5 Re: Help Me ! » Pls expand this for me » 2007-03-08 23:09:40

Can someone else expand this for me pls?

#6 Help Me ! » Pls expand this for me » 2007-03-08 18:19:40

renjer
Replies: 7

√ (4+∈²)

where ∈ is a variable (u can call it E if u like). I know its the binomial expansion but i can't seem to do it.

#7 Re: Help Me ! » Row reduced echelon form » 2006-06-14 00:16:35

Oh, actually I was wanting an easy way to get to reduced row echelon form, not just the normal echelon form. It's just sometimes driving me crazy. It's always like I've reduced an element in the matrix to zero, but because of another row operation, the zero becomes a number again, and I'll be going around in circles.

And this row reduction to reduced row echelon form, is for me to find eigenvectors.

#8 Help Me ! » Row reduced echelon form » 2006-06-13 22:10:59

renjer
Replies: 5

Reducing matrices to row echelon form is easy, however, most of the time I seem to go around in circles.

Take this matrix for example:

1   1   1
1   2   -2
1   -2   2

What is the easiest way to go, and how do you know what to do?

#10 Help Me ! » Is there any easy way to calculate Principal Unit Normal Vectors? » 2006-06-11 19:14:30

renjer
Replies: 2

Unit Tangent is easy to get. But when I get to unit normal, it kinda seems too difficult sometimes, particularly when you're trying to find T'.

Or when I try to use the tangential and normal accelerations (a=aT'+v^2KN) formula, that can get very hard too. (where a is the acceleration, T is the unit tangent vector, v is the velocity, K is the curvature and N is the unit normal).

So does anyone know a simpler way of doing this?

#11 Help Me ! » Probably the Chain Rule » 2006-06-07 15:22:48

renjer
Replies: 2

If x=y=100 and increasing at the rate of 1 per second, z=200, decreasing at the rate of 2 per second. Is R decreasing or increasing and at what rate?

I don't know how to do this question because R is not defined as R(x,y,z) but rather as 1/R. What do I do with this?

Btw I still don't know how to use the math tags. I tried encasing in

tag but the output was [math?] without my equations.

#12 Re: Help Me ! » Vector Space and Subset » 2006-06-04 18:49:28

Apply Gram Schmidt process to the power functions 1,t,t^2,t^3,t^4,t^5 to obtain the orthogonal bases of P1,P2,P3 and P4.

I don't think I know how to apply Gram-Schmidt for this one. What I know is how to apply Gram Schmidt for bases eg:

f1=(1,0,0)
f2=(1,1,1)

However when it comes to power functions, I'm stuck.

This is another part of the vector space and subset question.

Thanks for helping.

#13 Help Me ! » Vector Space and Subset » 2006-06-04 01:36:33

renjer
Replies: 4

Suppose P represents the vector space of all real polynomials and that for n=0,1,2... Pn denotes the subspace of P consisting of all polynomials of degree at most n. Suppose that the inner producr on P is defined by:

(f,g)=S-1 to 1 f(t)g(t) dt (where S is the integral sign, I don't know how to use the tags yet)

Explain why the power functions 1,t,t^2, t^3, ..., t^n form a basis of Pn.

Some of my friends have tried solving this question by using some really complex methods (Cauchy-Schwarz inequality etc) that are 2-3 pages long! I don't agree with them. I think, since 1,t,t^2, t^3,..., t^n is a polynomial, and P represents the vector space of all real polynomials, so, by logic the functions form a basis of Pn, right?

Btw, does anyone know any easy way to row reduce a complex matrix to find eigenvectors ie. :

F4=1/2 (1   1   1   1)
             1   i  -1   -i
             1  -1  1   -1
             1  -i   -1   i

1/2 times the matrix 4 X 4. I hope you can read it.

Eigenvalues=1,-1, i, 1

After doing eg F4-I, I have to do row reduction to find eigenvectors, and the problem is, it's tedious.

#14 Re: Help Me ! » Differential Equation » 2006-05-30 12:48:30

I've just learnt another way of solving DEs from lecture notes from another university.

But numen, I've never heard of solving using complex functions.

#15 Re: Help Me ! » Proving Linear Algebra » 2006-05-29 11:28:58

Let me rephrase that, I made some mistakes in my original post.

#16 Help Me ! » Proving Linear Algebra » 2006-05-29 03:39:58

renjer
Replies: 5

Prove that if norm(u X v)=0 then u.v=a norm(v)^2 where a is any constant.

I know that both u and v are parallel vectors and that norm(u X v) sin x = 0
Then I got stuck.

Anyone knows any good resources for me to learn linear algebra (preferably from the basics, with exercises and answers)? I'm finding it v hard to understand this topic.

Thanks.

#17 Re: Help Me ! » Differential Equation » 2006-05-28 01:22:12

Yeah DEs are actually very easy, just that sometimes I do not know the rules.

So anyone know how to answer my original question?

#18 Re: Help Me ! » Differential Equation » 2006-05-27 21:17:01

The answer seems like the one I had above. Anyway, thanks for showing me another method to solve DEs.

The next question goes: y''+y'+2y=t^2+e^-t+cos t.

Do I just find y''+y'+2y'=cos t? I've already calculated for t^2 and e^-t as was shown by numen. Then after I get all these, I just add them together with A and B. Is it right?

#19 Re: Help Me ! » Doing math in university? » 2006-05-27 20:21:40

Maths HAS loads of work, particularly when you get to advanced maths such as what I'm doing now. Actually there is a much harder maths out there called Fourier Analysis and Signal Processing. Last year I heard that no one passed that unit!

As most people here have said, physics and maths go hand in hand. Even biology needs maths (to model the behaviour of enzymes for example). One of my biology lecturers always complains that students in his class can't master basic calculus!

#20 Help Me ! » Differential Equation » 2006-05-27 20:08:24

renjer
Replies: 10

I don't know whether I'm wrong or not, but I get different answers from Scientific Workplace when I do this Differential Equation:

y''+3y'+2y=e^(-t)

Thanks for helping.

#21 Re: Maths Teaching Resources » is maths hard? » 2006-05-19 03:02:44

I think calculus is okay (some parts are hard eg vector calculus) but linear algebra and advanced matrices are almost intolerable.

#22 Maths Is Fun - Suggestions and Comments » Linear Algebra and Matrices » 2006-05-19 02:51:10

renjer
Replies: 0

Does anyone know where to find worksheets on Linear Algebra and Matrices?

(projection theory, vector spaces, kernel, inner product, cauchy-schwarz, gram-schmidt, fourier and haar bases for linear algebra. Hadamard matrices, real and imaginary matrices, adjoints, unitary matrices etc for matrices)

I have a feeling that these sections are the hardest of all in all of the maths that I've learnt this semester (I learnt about vectors, partial derivatives, multiple integrals, vector calculus and this section) because it is so abstract, and worse, I don't have any references to them! That's why I'm looking for resources for me to practise these problems if anyone knows any.

#23 Re: Help Me ! » Bart Simpson Rocks » 2006-05-19 02:43:24

Bart Simpson is LAZY. Math is not.
Math: 3, Bart Simpson: 0

#24 Re: Help Me ! » Lagrange » 2006-05-15 00:41:20

Then how can I relate that to Lagrange multipliers? I know there is supposed to be 2 equations f(x,y,z) and g(x,y,z) but now I don't know which two equations can I use.

#25 Help Me ! » Lagrange » 2006-05-14 01:38:14

renjer
Replies: 3

Use Lagrange multipliers to find the minimum distance from the point (5,5,4) to the paraboloid z=4-x^2-y^2.

I know a lot about Lagrange multipliers, they're quite easy, but the problem is, how do you find the distance from a point in space to a surface?

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