2025 HCI Promo Q11

2025 HCI Promo Q11

Junior College 1
14 marks

The curve \(C_3\) has parametric equations

    1. The point \(P\) travels along the curve \(C_3\) with its \(x\)-coordinate decreasing at a constant rate of 5 units per second. Find the rate of change of its \(y\)-coordinate when \(x=\dfrac{1}{4}\).[4]
    2. The distance between two points along a curve is the arc-length.\n\nThe arc-length between two points on \(C_3\), where \(p=\alpha\) and \(p=\beta\), is given by the formula \(\left|\int_{\alpha}^{\beta}\sqrt{\left(\dfrac{dx}{dp}\right)^2+\left(\dfrac{dy}{dp}\right)^2}\,dp\right|.\)\n\nFind the total length of the curve from the point \(A(-3,-6)\) to \(B(1,0)\).[3]
  1. Find the equation of the tangent to \(C_3\) at \(p=1\). Show algebraically that this tangent does not cut \(C_3\) again.[5]
  2. Find the cartesian equation of \(C_3\), expressing your answer in the form \(y^2=\mathrm{f}(x)\).[2]

Solution:

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Answer:(a)(i) \(-\dfrac{25\sqrt3}{12}\text{ units s}^{-1}\) (a)(ii) \(8.10\text{ units}\) (b) \(y=x\) (c) \(y^2=x^2(1-x)\)

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