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Figure 1 shows a sketch of the curve C with equation y = f(x) - Edexcel - A-Level Maths Pure - Question 11 - 2013 - Paper 2

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Question 11

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Figure 1 shows a sketch of the curve C with equation y = f(x). The curve C passes through the point (−1, 0) and touches the x-axis at the point (2, 0). The curve C... show full transcript

Worked Solution & Example Answer:Figure 1 shows a sketch of the curve C with equation y = f(x) - Edexcel - A-Level Maths Pure - Question 11 - 2013 - Paper 2

Step 1

The equation of the curve C can be written in the form y = x³ + ax² + bx + c

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Answer

To find the coefficients a, b, and c, we utilize the conditions given:

  1. Since the curve passes through the point (−1, 0):
    Substituting x = -1 and y = 0 into the equation gives:

    0=(1)3+a(1)2+b(1)+c0 = (-1)^3 + a(-1)^2 + b(-1) + c
    0=1+ab+c0 = -1 + a - b + c
    Thus, we have:
    ab+c=1ag1a - b + c = 1 ag{1}

  2. Since the curve touches the x-axis at the point (2, 0):
    Substituting x = 2 and y = 0 gives:

    0=(2)3+a(2)2+b(2)+c0 = (2)^3 + a(2)^2 + b(2) + c
    0=8+4a+2b+c0 = 8 + 4a + 2b + c
    Therefore:
    4a+2b+c=8ag24a + 2b + c = -8 ag{2}

  3. The curve has a maximum at the point (0, 4):
    Substituting x = 0 and y = 4 gives:

    4=(0)3+a(0)2+b(0)+c4 = (0)^3 + a(0)^2 + b(0) + c
    Hence, we find:
    c=4ag3c = 4 ag{3}

Using (3) in (1) and (2): From (1):
ab+4=1a - b + 4 = 1
ab=3ag4a - b = -3 ag{4}

From (2):
4a+2b+4=84a + 2b + 4 = -8

ightarrow 2a + b = -6 ag{5}$$ Now, solving equations (4) and (5): From (4): $$b = a + 3$$ Substituting into (5): $$2a + (a + 3) = -6$$ $$3a + 3 = -6$$ Thus, $$3a = -9 ightarrow a = -3$$ Substituting back to find b: $$b = -3 + 3 = 0$$ Therefore, the values of a, b, and c are: - a = -3 - b = 0 - c = 4.

Step 2

Sketch the curve with equation y = f^{-1}(x) in the space provided

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Answer

To sketch the inverse curve y = f^{-1}(x):

  1. The curve will be a reflection of the original curve across the line y = x.
  2. Identify key coordinates where the original curve crosses the axes:
    • The original crosses the x-axis at (2, 0) and the y-axis at (0, 4).
    • Reflect these points:
      • (0, 4) becomes (4, 0)
      • (2, 0) becomes (0, 2)
  3. The maximum point at (0, 4) is reflected to (4, 0).
  4. Draw the inverse curve through these points, ensuring to maintain the general shape of the original curve while reflecting across y = x.

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