Section 2.1

Hi! Today's section was on perpendicularity.
perpendicular- lines, rays, or segments that intersect to form right angles
intersect- having at least one point in common. (though the intersection may not be labeled as a point)

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AB _I_ CD

This means line AB is perpendicular to line CD. Sorry the perpendicular sign is a bit rough. It should look like this:

*The relationship "is perpendicular to" is symmetrical! (but not reflexive or transitive)*

You can NOT assume perpendicularity from a diagram.

                         As you can see, these lines appear perpendicular. However, because there is no indication that they are, you can not assume anything!

                           This is the exact same picture as before, except now there is a square to indicate a right angle, meaning that these lines definitely are perpendicular!

A couple more things about perpendicular lines:

Perpendicular --> RIGHT ANGLES, not 90 degrees!

2 lines are perpendicular IF AND ONLY IF (<-->) they intersect to form right angles.

If 2 lines intersect and DONT from right angles, they are not perpendicular.

Lastly, we talked about a few important fromulas for the coordinate plane.

First was the slope formula:

This can also be decribed as rise over run or delta y over delta x

Perpendicular lines have oppsite slopes such as y=-2x and y=1/2x

The next formula was the midpoint formula, which is:

or the average of the x coordinates over the average of the y coordinates

The final formula was the distance formula:

Here are some facts about horizontal and vertical lines:

horizontal line:

slope: 0

equation: y=a

vertical line:

slope: undefined

equation: x=b

And thats what we learned! Sorry for the rough pictures, I couldnt figure out the fancy math helper thing...

Bye! Katie <3