2025 VJC Promo Q10

2025 VJC Promo Q10

Junior College 1
10 marks

Do not use a calculator in answering this question.

  1. One of the roots of the equation \(2x^3-5x^2+22x-10=0\) is \(\frac{1}{2}\). Find the other two roots of the equation.[3]
  2. The complex number \(z\) is given by \(z=a+bi\), where \(a\) and \(b\) are real numbers such that \(a<0\) and \(b>0\). It is also given that \(\arg(z)=\theta\). In an Argand diagram, points \(P\) and \(Q\) represent \(z\) and \(iz\) respectively.
    1. On an Argand diagram, mark point \(P\), indicating \(\arg(z)\). On the same diagram, mark point \(Q\), showing the relationship between the two points.[2]
    2. Hence, find \(\arg(iz)\) in terms of \(\theta\).[1]
  3. Showing your working, find the complex numbers \(v\) and \(w\) which satisfy the simultaneous equations. \(\begin{aligned}2v-iw&=3\\(1+2i)v+2w&=5+i\end{aligned}\) Give your answers in the form \(x+iy\) where \(x\) and \(y\) are real numbers.[4]

Solution:

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Answer:Roots \(1\pm3i\); \(\arg(iz)=\theta-\dfrac{3\pi}{2}\); \(v=3+i,w=2-3i\)

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