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  1. leehuan

    Weird? vectors question

    $In two dimensions, let $\textbf{a}=\left[\begin{matrix}a_1\\a_2\end{matrix}\right]$ and $\textbf{b}=\left[\begin{matrix}b_1\\b_2\end{matrix}\right]$ and consider the parallelogram spanned by $\textbf{a}$ and $\textbf{b} \textbf{Show}$ that a parametric vector form for the parallelogram is...
  2. leehuan

    Cross product

    Question is easy but I cannot find my mistake. $Find the shortest distance between the line through the points $(1,3,1), \, (1,5,-1)$ and the line through the points $(0,2,1), \, (1,2,-3) Not sure if this is the standard method but this is according to the method I was taught. \lambda, \mu...
  3. leehuan

    2016 HSC Exam timetables

    Are you happy?
  4. leehuan

    Dot product

    $Suppose I have these vectors:$\\ \overrightarrow { AB } =\left[ \begin{matrix} 2 \\ 2 \\ -1 \end{matrix} \right] \\ \overrightarrow { BC } =\left[ \begin{matrix} -1 \\ -1 \\ 5 \end{matrix} \right] \\ Ignore CA for now $I'm required to find the cosine of the internal angles of $\triangle...
  5. leehuan

    Parametrics and Polar curves

    Starting with a dumb question because I think my lecturer forgot to explicitly say how to. I know what the graph looks like already r=6\sin{\theta} But how do I convert this to Cartesian form lol
  6. leehuan

    Conditions on L'Hopital's rule

    I've forgotten why L'Hopitals breaks down for this. \lim_{x\rightarrow\infty}{\frac{x+\sin{x}}{x-\sin{x}}} Isn't it technically infty/infty
  7. leehuan

    Renewing MATLAB licence

    The MATLAB software I downloaded at home supposedly has a licence expiry date set within 12 days from now. How do I resolve this issue? (If there's already a post on this please link) Thanks
  8. leehuan

    Using determinants

    Already known: \det{\left( \begin{matrix} z & 1 & 2 \\ 1 & z & 3 \\ 1 & 1 & z+1 \end{matrix} \right) }=\left(z-1\right)\left({z}^{2}+2z-4\right) And hence solve: zx+y=2 x+zy=3 x+y=z+1 Can't draw the link between the statements. All I get is this: \text{By using the exact same...
  9. leehuan

    Proving determinant properties

    Let U1 and U2 be two nxn row-echelon matrices. Prove that det(U1)det(U2)=det(U1U2) So far... \\$Let the components of ${U}_{1}, U_{2}, U_{1}U_{2}$ respectively be ${u}_{ij},{v}_{ij},{a}_{ij}\\$ for some integers $i, j \in [1,n] \\$Since ${U}_{1}$ and ${U}_{2}$ are upper triangular:$\\\left| {...
  10. leehuan

    Don't understand the question's wording

    So the question just said to show that Q = (cos, -sin // sin cos) is orthogonal, and that x (in R2) and Qx are equidistant. Easy. What does it mean here to say that Q acts as a rotation on R2?
  11. leehuan

    More differentiation qns

    $Let $f$ be continuous on $[a,b]$. Prove that there exists $c\in\(a,b)$ such that$\\ \int_{a}^{b}{f(t)dt}=f(c)(b-a) When I tried experimenting with the MVT I found something like this: f(b)-f(a)=f^{\prime}(c)(b-a) However they gave a hint and I have no idea how to apply it. $Hint: Let...
  12. leehuan

    Can this be contradicted?

    If f' is (continuous, differentiable and) monotone, f always concaves the same way
  13. leehuan

    Mean Value Theorem proofs

    So I got part a) out. Need only a small starter on part b). But it's mainly cause of the process. Q: Use the MVT to prove that a) ln(1+x)<x for x>0 b) -ln(1-x)<x/(1-x) for 0<x<1 So for part a) I defined f:[0,x], f(t)=ln(1+t) and used the MVT to get ln(1+x)/x=1/c (for some c in (0,x)) So cause...
  14. leehuan

    Essential discontinuity - terminology

    These are just when at least one left or right side limit is undefined right? So obviously sin(1/x) has this problem at x=0 due to the rapidly oscillating behaviour. Would vertical asymptotes also get classified as this?
  15. leehuan

    Ma...tri...ces..

    This is preposterous... What's the easiest way to do this question? $If $A$ and $B$ are square matrices such that $AB=BA$ show that $\\(A-B)(A+B)={A}^{2}-{B}^{2} Writing out the components takes way too long
  16. leehuan

    Reasoning

    Posting this in the 2U section as it's still within the scope of the course (even though it's just my homework). $The function $f$ is defined by $f(x)={x}^{2}-4x+3$ for $0 < x \le 3$, $f(-x)=-f(x)$ for all $x$ and $f(x+6)=f(x)$ for all $x$. I have the graph in front of me so I can pretty much...
  17. leehuan

    Starting little-oh notation

    LaTeX is broken again so I won't use it Am I doing this correctly? Q: As h->0, show that (explain why) sin(x+h)=sinx+hcosx+o(h) A: Let g(x)=sin(x+h)-sinx-hcosx Need |g(x)|<=K|h| for all K>0 i.e. |sin(x+h)-sinx-hcosx|<=K|h| <=> | (sin(x+h)-sinx)/h - cosx| <= K (as h neq 0) LHS = |...
  18. leehuan

    Diagram problems

    Can't start this question cause I don't know what I'm looking at. How would I simulate it? $In this problem we shall calculate the area of a spherical triangle. Consider the surface of a sphere of unit radius of area $4\pi$. A great circle on a sphere is the intersection of that sphere with a...
  19. leehuan

    Lost in wording with matrices

    Just start me off please. No need to complete the question. $Assume 3 countries $A, B, $ and $C$ trade with one another and no-one else, that a common currency is used and that each country's total income comes from trade with the others or sales to itself and nothing else.$ \\ A$ spends...
  20. leehuan

    First fundamental theorem of calculus - examinable?

    In other words, could you be directly asked on one of the following in 2U (and I guess any other relevant HSC courses)? \\\frac{d}{dx}\int_{c}^{x}{f(t)\,dt}=f(x) $+ a chain rule application:$\\\frac{d}{dx}\int_{c}^{g(x)}{f(t)\,dt}=f'(g(x))g'(x)
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