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Here is a sketch of the line L - Edexcel - GCSE Maths - Question 14 - 2021 - Paper 2

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Question 14

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Here is a sketch of the line L. The points P(-6, 0) and Q(0, 3) are points on the line L. The point R is such that PQR is a straight line and PQ:QR = 2:3. (a) Find... show full transcript

Worked Solution & Example Answer:Here is a sketch of the line L - Edexcel - GCSE Maths - Question 14 - 2021 - Paper 2

Step 1

(a) Find the coordinates of R.

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Answer

To find the coordinates of point R, we first need to determine the distance between points P and Q.

  1. Calculate the distance PQ: Using the distance formula: d=(x2x1)2+(y2y1)2d = \sqrt{(x_2 - x_1)^2 + (y_2 - y_1)^2} where P(-6, 0) and Q(0, 3).

    PQ=(0(6))2+(30)2=(6)2+(3)2=36+9=45=35PQ = \sqrt{(0 - (-6))^2 + (3 - 0)^2} = \sqrt{(6)^2 + (3)^2} = \sqrt{36 + 9} = \sqrt{45} = 3\sqrt{5}

  2. Find the distances based on the ratio: Since PQ : QR = 2 : 3, we find QR:

    • Let the total distance be divided into 5 equal parts (2 + 3).

    • Find the lengths:

      • Length of PQ: PQ=25×(35)=655PQ = \frac{2}{5} \times (3\sqrt{5}) = \frac{6\sqrt{5}}{5}
        • Length of QR: QR=35×(35)=955QR = \frac{3}{5} \times (3\sqrt{5}) = \frac{9\sqrt{5}}{5}
  3. Calculate the coordinates of R: We can find R by moving from Q to R at the coordinates Q(0, 3).

    To find coordinates of R, we need to find the direction vector of PQ, which is:

    • Direction from P to Q: (0(6),30)=(6,3) (0 - (-6), 3 - 0) = (6, 3)

    • Normalize this direction vector: V=(6,3)(62+32)=(6,3)35V = \frac{(6, 3)}{\sqrt{(6^2 + 3^2)}} = \frac{(6, 3)}{3\sqrt{5}}

    • Moving from Q(0, 3) towards R in the same direction:

      Let's move by the length QR:

      R=Q+95(6,3)35=(0,3)+(10815,5415)=(10815,12915)R = Q + \frac{9}{5} \cdot \frac{(6, 3)}{3\sqrt{5}} = (0, 3) + (\frac{108}{15}, \frac{54}{15}) = (\frac{108}{15}, \frac{129}{15})

So, the coordinates of point R are approximately: R(10815,12915)R(\frac{108}{15}, \frac{129}{15}).

Step 2

(b) Find an equation of the line that is perpendicular to L and passes through Q.

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Answer

To find the equation of the line perpendicular to L and passing through Q(0, 3), we need to follow these steps:

  1. Find the gradient of line L:

    • Using the points P(-6, 0) and Q(0, 3):

      mL=y2y1x2x1=300(6)=36=12m_{L} = \frac{y_2 - y_1}{x_2 - x_1} = \frac{3 - 0}{0 - (-6)} = \frac{3}{6} = \frac{1}{2}

  2. Calculate the gradient of the perpendicular line:

    • Since the product of the gradients of two perpendicular lines is -1:

      mperpendicular=1mL=112=2m_{perpendicular} = -\frac{1}{m_{L}} = -\frac{1}{\frac{1}{2}} = -2

  3. Use point-slope form to write the equation:

    • Using point-slope form: yy1=m(xx1)y - y_1 = m(x - x_1)

    • Substituting the coordinates of Q(0, 3) and the gradient:

      y3=2(x0)y - 3 = -2(x - 0)

    • Rearranging gives: y=2x+3y = -2x + 3

Thus, the equation of the line that is perpendicular to L and passes through Q is: y=2x+3y = -2x + 3.

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