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Consider the functions $f(x) = ext{sin} x$ and $g(x) = x ext{sin} x$ - HSC - SSCE Mathematics Extension 2 - Question 10 - 2018 - Paper 1

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Consider-the-functions-$f(x)-=--ext{sin}-x$-and-$g(x)-=-x--ext{sin}-x$-HSC-SSCE Mathematics Extension 2-Question 10-2018-Paper 1.png

Consider the functions $f(x) = ext{sin} x$ and $g(x) = x ext{sin} x$. The x-coordinate of each stationary point of $f(x)$ is very close to the x-coordinate of a s... show full transcript

Worked Solution & Example Answer:Consider the functions $f(x) = ext{sin} x$ and $g(x) = x ext{sin} x$ - HSC - SSCE Mathematics Extension 2 - Question 10 - 2018 - Paper 1

Step 1

Which statement is always true?

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Answer

Since f(x)=extsinxf(x) = ext{sin} x and g(x)=xextsinxg(x) = x ext{sin} x, we must analyze the stationary points of both functions.

  1. Finding stationary points:

    • The stationary points of f(x)=extsinxf(x) = ext{sin} x occur where the derivative f(x)=extcosx=0f'(x) = ext{cos} x = 0, which gives us the points x = rac{ rac{ ext{(2n+1) oindent ext{)}}}{2} ext{ where } n ext{ is an integer.}
  2. **Behavior of stationary points for g(x)=xextsinxg(x) = x ext{sin} x:

    • For g(x)g(x), we find stationary points via differentiated, giving g(x)=extsinx+xextcosx=0.g'(x) = ext{sin} x + x ext{cos} x = 0. The solutions to this equation will provide points bb.
  3. **Comparing points aa and bb:

    • Given that the stationary points of f(x)f(x) are close to those of g(x)g(x), the value of a<b|a| < |b| is the only statement that holds true, since g(x)g(x) adds the multiplicative factor of xx. Hence, option C is always true.

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