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The functions f and g are defined by f : x ↦ ln(2x-1), x ∈ ℝ, x > rac{1}{2}, g : x ↦ rac{2}{x-3}, x ∈ ℝ, x ≠ 3 - Edexcel - A-Level Maths Pure - Question 7 - 2007 - Paper 5

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The-functions-f-and-g-are-defined-by--f-:-x-↦-ln(2x-1),---------------x-∈-ℝ,-x->--rac{1}{2},--g-:-x-↦--rac{2}{x-3},---------------x-∈-ℝ,-x-≠-3-Edexcel-A-Level Maths Pure-Question 7-2007-Paper 5.png

The functions f and g are defined by f : x ↦ ln(2x-1), x ∈ ℝ, x > rac{1}{2}, g : x ↦ rac{2}{x-3}, x ∈ ℝ, x ≠ 3. (a) Find the exact v... show full transcript

Worked Solution & Example Answer:The functions f and g are defined by f : x ↦ ln(2x-1), x ∈ ℝ, x > rac{1}{2}, g : x ↦ rac{2}{x-3}, x ∈ ℝ, x ≠ 3 - Edexcel - A-Level Maths Pure - Question 7 - 2007 - Paper 5

Step 1

Find the exact value of fg(4)

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Answer

To find fg(4), we first calculate g(4):

g(4)=243=2.g(4) = \frac{2}{4-3} = 2.

Next, we substitute this result into f:

f(g(4))=f(2)=ln(221)=ln(3).f(g(4)) = f(2) = \ln(2 \cdot 2 - 1) = \ln(3).

Thus, the exact value of fg(4) is ( \ln(3) ).

Step 2

Find the inverse function f^{-1}(x), stating its domain

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Answer

To find the inverse function f^{-1}(x), we start with:

y=ln(2x1).y = \ln(2x-1).

Exponential both sides gives:

ey=2x1,e^y = 2x - 1, which can be rearranged to:

x=ey+12.x = \frac{e^y + 1}{2}.

Thus, the inverse function is:

f1(x)=ex+12,f^{-1}(x) = \frac{e^x + 1}{2}, with the domain of (f^{-1}(x)) being all real numbers ( \mathbb{R} ) since the range of f is ( \mathbb{R} ).

Step 3

Sketch the graph of y = |g(x)|

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Answer

To sketch the graph of (y = |g(x)|), we first determine the vertical asymptote and y-intercept:

  1. Vertical Asymptote: Set the denominator equal to zero: x3=0x=3.x - 3 = 0 \Rightarrow x = 3.

  2. Y-intercept: Evaluate (g(0):) g(0)=203=23,g(0) = \frac{2}{0-3} = -\frac{2}{3}, therefore (|g(0)| = \frac{2}{3}.$$

The graph will show a vertical asymptote at (x = 3) and will cross the y-axis at (y = \frac{2}{3}).

Step 4

Find the exact values of x for which \frac{2}{|x-3|} = 3

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Answer

To solve (\frac{2}{|x-3|} = 3), we begin by manipulating the equation:

  1. Multiply both sides by (|x-3|): 2=3x3.2 = 3|x-3|.

  2. Solve for (|x-3|): x3=23.|x-3| = \frac{2}{3}.

  3. Two cases arise:

    • Case 1: (x - 3 = \frac{2}{3}) \Rightarrow (x = 3 + \frac{2}{3} = \frac{11}{3}.
    • Case 2: (x - 3 = -\frac{2}{3}) \Rightarrow (x = 3 - \frac{2}{3} = \frac{7}{3}.

Thus, the exact values of (x) are (\frac{11}{3}) and (\frac{7}{3}).

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