Perpendicular Lines

Intersect to form a right angle (90 degress)!

Perpendicular lines can be found all around you!

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What do we know about the slopes of perpendicular lines?

  • They are opposite reciprocals!
  • Remember: Flip it & change the sign!
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Let's try an example!

Write the equation of the line perpendicular to the line below passing through the point (0, 4).

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Step 1: Find the slope of the given line.

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Step 2: Find the opposite reciprocal, this will be the slope for Step 3 & 4.

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Step 3: Substitute the slope of the given line, and the x- & y- values of the given point into the equation y = mx + b, and solve for b.

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Step 4: Substitute m & b into y = mx + b.

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Let's look at another example!

Write the equation of the line perpendicular to y = (-1/2)x - 5 passing through the point (-4, 6).

Step 1: Find the slope of the given line.

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Step 2: Find the opposite reciprocal, this will be the slope for Step 3 & 4.

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Step 3: Substitute the slope of the given line, and the x- & y- values of the given point into the equation y = mx + b, and solve for b.

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Step 4: Substitute m & b into y = mx + b.

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