Find the Line Equation Through Points (2,8) and (6,1): Coordinate Geometry

Slope-Intercept Form with Mixed Number Coefficients

Find the equation of the line passing through the two points (2,8),(6,1) (2,8),(6,1)

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Find the algebraic representation of the function
00:04 We'll use the formula to find a line equation using 2 points
00:16 In each point the left number represents X-axis and the right Y
00:30 We'll substitute the points according to the given data and find the slope
00:42 This is the line's slope
00:46 Now we'll use the line equation
00:57 We'll substitute the point according to the given data
01:03 We'll substitute the slope and solve to find the intersection point (B)
01:17 We'll isolate the intersection point (B)
01:27 This is the intersection point with the Y-axis
01:31 Now we'll substitute the intersection point and slope in the line equation
01:46 And this is the solution to the question

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

Find the equation of the line passing through the two points (2,8),(6,1) (2,8),(6,1)

2

Step-by-step solution

To find the equation of the line passing through the points (2,8) (2,8) and (6,1) (6,1) , follow the steps below:

  • Step 1: Calculate the slope m m .
    The formula for the slope m m is:

m=y2y1x2x1=1862=74 m = \frac{y_2 - y_1}{x_2 - x_1} = \frac{1 - 8}{6 - 2} = \frac{-7}{4}

  • Step 2: Use the point-slope form to write the equation of the line.
    The point-slope form of a line is given by:

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

Using the point (2,8)(2,8):

y8=74(x2) y - 8 = -\frac{7}{4}(x - 2)

  • Step 3: Simplify to the slope-intercept form.
    Distribute the slope and rearrange to find y y :

y8=74x+72 y - 8 = -\frac{7}{4}x + \frac{7}{2}

Add 8 to both sides to solve for y y :

y=74x+72+8 y = -\frac{7}{4}x + \frac{7}{2} + 8

Convert 8 to a fraction with a denominator of 2:

y=74x+72+162 y = -\frac{7}{4}x + \frac{7}{2} + \frac{16}{2}

Simplify the addition:

y=74x+232 y = -\frac{7}{4}x + \frac{23}{2}

To convert 23/2 23/2 into mixed number form: 232=1112 \frac{23}{2} = 11 \frac{1}{2}

Thus, the equation in slope-intercept form is: y=74x+1112 y = -\frac{7}{4}x + 11 \frac{1}{2}

Therefore, the equation of the line passing through these points is y=134x+1112 y = -1\frac{3}{4}x + 11\frac{1}{2} , which matches the correct choice in the multiple-choice answers.

3

Final Answer

y=134x+1112 y=-1\frac{3}{4}x+11\frac{1}{2}

Key Points to Remember

Essential concepts to master this topic
  • Slope Formula: Use m=y2y1x2x1 m = \frac{y_2 - y_1}{x_2 - x_1} to find rate of change
  • Point-Slope Method: Apply yy1=m(xx1) y - y_1 = m(x - x_1) using (2,8) (2,8) and m=74 m = -\frac{7}{4}
  • Verification: Substitute both points into final equation: 8=74(2)+232 8 = -\frac{7}{4}(2) + \frac{23}{2} gives 8=8 8 = 8

Common Mistakes

Avoid these frequent errors
  • Calculating slope with coordinates in wrong order
    Don't use x2x1y2y1=6218=47 \frac{x_2 - x_1}{y_2 - y_1} = \frac{6-2}{1-8} = \frac{4}{-7} = wrong slope! This flips the fraction and gives completely incorrect coefficients. Always put y-coordinates in numerator and x-coordinates in denominator: y2y1x2x1 \frac{y_2 - y_1}{x_2 - x_1} .

Practice Quiz

Test your knowledge with interactive questions

Look at the function shown in the figure.

When is the function positive?

xy-4-7

FAQ

Everything you need to know about this question

Why is the slope negative when both points seem to go up?

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Look carefully at the y-coordinates! Point (2,8) (2,8) has y = 8, while (6,1) (6,1) has y = 1. As x increases from 2 to 6, y decreases from 8 to 1, creating a downward slope.

How do I convert 74 -\frac{7}{4} to a mixed number?

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Divide 7 by 4: 7÷4=1 7 ÷ 4 = 1 remainder 3 3 . So 74=134 \frac{7}{4} = 1\frac{3}{4} . With the negative sign: 74=134 -\frac{7}{4} = -1\frac{3}{4} .

Can I use the other point (6,1) (6,1) instead of (2,8) (2,8) ?

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Absolutely! Either point works in the point-slope form. Using (6,1) (6,1) : y1=74(x6) y - 1 = -\frac{7}{4}(x - 6) will give you the same final equation after simplifying.

Why do we need to add fractions with different denominators?

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When adding 72+8 \frac{7}{2} + 8 , convert 8 to the same denominator: 8=162 8 = \frac{16}{2} . Then: 72+162=232 \frac{7}{2} + \frac{16}{2} = \frac{23}{2} . This keeps our math precise!

How do I check if my final answer is correct?

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Substitute both original points into your equation. For (2,8) (2,8) : 8=134(2)+1112=312+1112=8 8 = -1\frac{3}{4}(2) + 11\frac{1}{2} = -3\frac{1}{2} + 11\frac{1}{2} = 8 ✓. For (6,1) (6,1) : 1=134(6)+1112=1012+1112=1 1 = -1\frac{3}{4}(6) + 11\frac{1}{2} = -10\frac{1}{2} + 11\frac{1}{2} = 1

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