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The line $y = x + 2$ meets the curve $x^2 + 4y^2 - 2x = 35$ at the points A and B as shown in Figure 2 - Edexcel - A-Level Maths Pure - Question 6 - 2013 - Paper 2

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The-line-$y-=-x-+-2$-meets-the-curve-$x^2-+-4y^2---2x-=-35$-at-the-points-A-and-B-as-shown-in-Figure-2-Edexcel-A-Level Maths Pure-Question 6-2013-Paper 2.png

The line $y = x + 2$ meets the curve $x^2 + 4y^2 - 2x = 35$ at the points A and B as shown in Figure 2. (a) Find the coordinates of A and the coordinates of B. (b)... show full transcript

Worked Solution & Example Answer:The line $y = x + 2$ meets the curve $x^2 + 4y^2 - 2x = 35$ at the points A and B as shown in Figure 2 - Edexcel - A-Level Maths Pure - Question 6 - 2013 - Paper 2

Step 1

Find the coordinates of A and the coordinates of B.

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Answer

To find the points A and B where the line intersects the curve, we substitute the equation of the line into the equation of the ellipse.

  1. Substitute y=x+2y = x + 2 into the curve equation: x2+4(x+2)22x=35x^2 + 4(x + 2)^2 - 2x = 35

  2. Expand the equation: x2+4(x2+4x+4)2x=35x^2 + 4(x^2 + 4x + 4) - 2x = 35 x2+4x2+16x+162x=35x^2 + 4x^2 + 16x + 16 - 2x = 35 5x2+14x+1635=05x^2 + 14x + 16 - 35 = 0 5x2+14x19=05x^2 + 14x - 19 = 0

  3. Use the quadratic formula x=b±b24ac2ax = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} where a=5a = 5, b=14b = 14, and c=19c = -19:

    x=14±1424(5)(19)2(5)x = \frac{-14 \pm \sqrt{14^2 - 4(5)(-19)}}{2(5)} x=14±196+38010x = \frac{-14 \pm \sqrt{196 + 380}}{10} x=14±57610x = \frac{-14 \pm \sqrt{576}}{10} x=14±2410x = \frac{-14 \pm 24}{10}

  4. Solve for xx:

    • First root: x1=1010=1x_1 = \frac{10}{10} = 1
    • Second root: x2=3810=3.8x_2 = \frac{-38}{10} = -3.8
  5. Now substitute these xx values back into the line equation to find yy:

    • For x=1x = 1: y1=1+2=3y_1 = 1 + 2 = 3
    • For x=3.8x = -3.8: y2=3.8+2=1.8y_2 = -3.8 + 2 = -1.8
  6. Thus, the coordinates of point A are (1,3)(1, 3) and the coordinates of point B are (3.8,1.8)(-3.8, -1.8).

Step 2

Find the distance AB in the form r√2 where r is a rational number.

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Answer

To find the distance ABAB, we can use the distance formula: d=(x2x1)2+(y2y1)2d = \sqrt{(x_2 - x_1)^2 + (y_2 - y_1)^2}

  1. Using the coordinates of points A (1,3)(1, 3) and B (3.8,1.8)(-3.8, -1.8):

    • x1=1,y1=3x_1 = 1, y_1 = 3
    • x2=3.8,y2=1.8x_2 = -3.8, y_2 = -1.8
  2. Substitute these values into the distance formula: d=((3.81)2+(1.83)2)d = \sqrt{((-3.8 - 1)^2 + (-1.8 - 3)^2)} =(4.8)2+(4.8)2= \sqrt{(-4.8)^2 + (-4.8)^2} =(23.04+23.04)= \sqrt{(23.04 + 23.04)} =46.08= \sqrt{46.08}

  3. Simplifying further, we find: d=46.08=(223.04)=22304100=24810=4.82d = \sqrt{46.08} = \sqrt{(2 \cdot 23.04)} = \sqrt{2 \cdot \frac{2304}{100}} = \sqrt{2} \cdot \frac{48}{10} = 4.8 \sqrt{2}

Therefore, the distance AB is 4.824.8 \sqrt{2}, where r=4.8r = 4.8.

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