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The point A(−6, 4) and the point B(8, −3) lie on the line L - Edexcel - A-Level Maths Pure - Question 5 - 2008 - Paper 2

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The point A(−6, 4) and the point B(8, −3) lie on the line L. (a) Find an equation for L in the form ax + by + c = 0, where a, b and c are integers. (b) Find the di... show full transcript

Worked Solution & Example Answer:The point A(−6, 4) and the point B(8, −3) lie on the line L - Edexcel - A-Level Maths Pure - Question 5 - 2008 - Paper 2

Step 1

Find an equation for L in the form ax + by + c = 0

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Answer

To find the equation of the line L passing through the points A(−6, 4) and B(8, −3), we first calculate the slope (m) using the formula:

m=y2y1x2x1=348(6)=714=12m = \frac{y_2 - y_1}{x_2 - x_1} = \frac{-3 - 4}{8 - (-6)} = \frac{-7}{14} = -\frac{1}{2}

With the slope known, we can use point-slope form to find the equation of the line. Using point A:

yy1=m(xx1)y - y_1 = m(x - x_1)

This gives us:

y4=12(x+6)y - 4 = -\frac{1}{2}(x + 6)

Expanding this, we find:

y4=12x3y - 4 = -\frac{1}{2}x - 3 y=12x+1y = -\frac{1}{2}x + 1

To write this in the standard form ax + by + c = 0, we rearrange:

12x+y1=0\frac{1}{2}x + y - 1 = 0

Multiplying through by 2 to eliminate the fraction, we obtain:

x+2y2=0x + 2y - 2 = 0

Thus, an acceptable equation for L in integer form is:

x+2y2=0x + 2y - 2 = 0

Step 2

Find the distance AB, giving your answer in the form k√5

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Answer

To find the distance between points A(−6, 4) and B(8, −3), we use the distance formula:

d=(x2x1)2+(y2y1)2d = \sqrt{(x_2 - x_1)^2 + (y_2 - y_1)^2}

Substituting in the coordinates of A and B:

d=(8(6))2+(34)2d = \sqrt{(8 - (-6))^2 + (-3 - 4)^2} =(8+6)2+(7)2= \sqrt{(8 + 6)^2 + (-7)^2} =142+72= \sqrt{14^2 + 7^2} =196+49= \sqrt{196 + 49} =245= \sqrt{245} =49×5= \sqrt{49 \times 5} =75= 7\sqrt{5}

Thus, the distance AB can be expressed as:

k=7, so the answer is 75k = 7\text{, so the answer is } 7\sqrt{5}

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