2024 SJI P2 Q8

2024 SJI P2 Q8

IB Year 5 | Grade 11
18 marks

A function is defined by \(\mathrm f(x)=\dfrac{x^2+20x+101}{x+10}\), where \(x\in\mathbb R\), \(x\neq-10\).

  1. Express \(\mathrm f(x)\) in the form \(ax+b+\dfrac c{x+10}\), where \(a,b,c\) are constants to be determined.[3]
  2. Write down the equations of the asymptotes of the graph \(y=\mathrm f(x)\).[2]
  3. Prove that the graph of \(y=\mathrm f(x)\) does not cut the \(x\)-axis.[3]
  4. Sketch the graph of \(y=\mathrm f(x)\), labelling clearly the equations of the asymptotes, the coordinates of the turning points and the intersections with the axes.[4]
  5. Solve the inequality \(\mathrm f(2x)\geq x\).[3]
  6. Hence solve \(\mathrm f(2\ln x)\geq\ln x\). Give your answers to 6 decimal places.[3]

Solution:

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Answer:(a) \(a=1,b=10,c=1\) (b) \(x=-10,y=x+10\) (c) Proved. (d) Turning points \((-11,-2),(-9,2)\); intercept \((0,10.1)\). (e) \(\dfrac{-15-\sqrt{23}}2\leq x\leq\dfrac{-15+\sqrt{23}}2\) or \(x>-5\). (f) \(0.000050\leq x\leq0.006084\) or \(x>0.006738\).

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