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Using Point-Slope Form to Write the Equation of a Line

1.14.1 Using Point-Slope Form to Write the Equation of a Line

1.14.1 • Using Point-Slope Form to Write the Equation of a Line

Warm Up

Your teacher will assign you one pair of the points shown.

  • Points for Line A: ( − 1 , 5 ) ( − 1 , 5 ) and ( 1 , 1 ) ( 1 , 1 )

  • Points for Line B: ( − 1 , − 1 ) ( − 1 , − 1 ) and ( 1 , − 5 ) ( 1 , − 5 )

Use your assigned points to find the following:

1.

Find the slope of the line.

Compare your answer:

Line A: slope: m = 1 − 5 1 − ( − 1 ) = − 2 m = 1 − 5 1 − ( − 1 ) = − 2

Line B: slope: m = − 5 − ( − 1 ) 1 − ( − 1 ) = − 2 m = − 5 − ( − 1 ) 1 − ( − 1 ) = − 2

Remember to use the slope formula to find the slope: m = y 2 − y 1 x 2 − x 1 m = y 2 − y 1 x 2 − x 1 .

2.

Write the equation of the line in slope-intercept form.

Compare your answer:

Line A: equation  y = − 2 x + 3 y = − 2 x + 3

Line B: equation y = − 2 x − 3 y = − 2 x − 3

Remember to use the point-slope form for the equation of the line to write the equation: y − y 1 = m 1 ( x − x 1 ) y − y 1 = m 1 ( x − x 1 ) . Write the equation in slope-intercept form y = m x + b y = m x + b , where the slope is m m and the y y -intercept is b b .

3.

Compare your equation to your partner’s equation. What were some things that were the same? What were some things that were different

Compare your answer:

Your answer may vary, but here are some samples.

  • Both lines have a negative slope.
  • Both lines have the same slope.
  • The y y -intercepts are different.
  • The y y -intercepts have opposite signs.