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Figure 1 shows a sketch of the curve with equation $y = \frac{2}{x}$, $x \neq 0$ - Edexcel - A-Level Maths Pure - Question 7 - 2013 - Paper 3

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Figure 1 shows a sketch of the curve with equation $y = \frac{2}{x}$, $x \neq 0$. The curve C has equation $y = \frac{2}{x} - 5$, $x \neq 0$, and the line l has equ... show full transcript

Worked Solution & Example Answer:Figure 1 shows a sketch of the curve with equation $y = \frac{2}{x}$, $x \neq 0$ - Edexcel - A-Level Maths Pure - Question 7 - 2013 - Paper 3

Step 1

Sketch and clearly label the graphs of C and l on a single diagram.

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Answer

To illustrate the graphs of both curves, we start by plotting the graph of the curve CC, which is defined by the function y=2x5y = \frac{2}{x} - 5. This function has a vertical asymptote at x=0x = 0 and a horizontal asymptote at y=5y = -5. The graph of the line ll defined by y=4x+2y = 4x + 2 will be a straight line that crosses the y-axis at (0,2)(0, 2) and has a slope of 4.

  • Coordinates of Intersections:
    • For curve CC:
      • xx-intercept: Set y=0y = 0: 0=2x5    2x=5    x=250 = \frac{2}{x} - 5 \implies \frac{2}{x} = 5 \implies x = \frac{2}{5}
        Thus, the x-intercept is at (25,0)\, (\frac{2}{5}, 0).
    • For line ll:
      • xx-intercept: Set y=0y = 0: 0=4x+2    4x=2    x=120 = 4x + 2 \implies 4x = -2 \implies x = -\frac{1}{2} Thus, the x-intercept is at (12,0)( -\frac{1}{2}, 0).
  • The y-intercept of CC can be found by substituting xx:
    • y=215=3y = \frac{2}{1} - 5 = -3 Thus, the y-intercept is at (0,3)(0, -3).

Step 2

Write down the equations of the asymptotes of the curve C.

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Answer

The equations of the asymptotes for curve C are:

  • Vertical Asymptote: x=0x = 0
  • Horizontal Asymptote: y=5y = -5

Step 3

Find the coordinates of the points of intersection of $y = \frac{2}{x} - 5$ and $y = 4x + 2$.

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Answer

To find the points of intersection, we set the functions equal to each other: 2x5=4x+2\frac{2}{x} - 5 = 4x + 2

  1. Rearranging gives: 2x=4x+7\frac{2}{x} = 4x + 7

  2. Multiplying both sides by xx (where x0x \neq 0) results in: 2=4x2+7x2 = 4x^2 + 7x

  3. Rearranging results in: 4x2+7x2=04x^2 + 7x - 2 = 0

  4. Applying the quadratic formula, we have: x=b±b24ac2a=7±7244(2)24x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} = \frac{-7 \pm \sqrt{7^2 - 4 \cdot 4 \cdot (-2)}}{2 \cdot 4}

  5. This simplifies to: x=7±49+328=7±818=7±98x = \frac{-7 \pm \sqrt{49 + 32}}{8} = \frac{-7 \pm \sqrt{81}}{8} = \frac{-7 \pm 9}{8}

Thus, we find two potential x values:

  • x1=28=14x_1 = \frac{2}{8} = \frac{1}{4}
  • x2=168=2x_2 = \frac{-16}{8} = -2
  1. Now substituting back to find corresponding yy values:
  • For x=14x = \frac{1}{4}: y=4(14)+2=1+2=3y = 4(\frac{1}{4}) + 2 = 1 + 2 = 3
  • For x=2x = -2: y=4(2)+2=8+2=6y = 4(-2) + 2 = -8 + 2 = -6

Thus, the points of intersection are:

  • (14,3)\left( \frac{1}{4}, 3 \right) and (2,6)(-2, -6).

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