We reviewed a ton of terms that you knew from previous years:

- right angle
- acute angle
- obtuse angle
- straight angle
- reflex angle
- right triangle
- scalene triangle
- isoceles triangle
- equilateral/equiangular triangle
- hypotenuse (of a right triangle)
- median (of a triangle)
- vertex
- side
- altitude
- perpendicular
- bisector
- perpendicular bisector :)

Those last few were the new learning today.

If a line has slope , any perpendicular line has slope , which is the negative reciprocal of .

If two perpendicular lines have slope and , then (if the lines aren’t horizontal and vertical).

A bisector is a line that intersects a line segment at its midpoint (cutting it into two equal pieces).

A perpendicular bisector is a line that intersects a line segment at its midpoint and is at 90 degress to that segment.

For example, suppose we have a segment with endpoints and .

The midpoint of that segment is . The slope of the segment is .

The perpendicular bisector passes through the point and has slope .

We can use the general form , substituting known values for , and :

and solve to get

Therefore the equation of the perpendicular bisector is .

No homework tonight.

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