Perpendicular Lines Lesson

Perpendicular Lines Lesson

What do we look for when lines are perpendicular?

• Look at the SLOPE!

• Has to be opposite reciprocal "Change the sign and flip the fraction"

• remember whole numbers go over one before you flip

Multiple Select

Check all the lines that are parallel to

 $y=-2x+5$  

•  $2x+y=16$  

•  $y=-2x+1$  

•  $y=2x-10$  

•  $x-2y=-6$  

Multiple Choice

If the equation is in standard form what do you have to do in order to get the slope?

• go down the slide

• pull the number off the x and that is your slope

• solve for slope intercept first

If you said solve for slope intercept first you are correct

 (or if you remember the "cheat method"

 $\frac{-x}{\text{}y}$  then you can use that)

Multiple Choice

Tell what the 2 equations are:

 $y=-2x\ \ \ \ and\ \ \ \ \ y=\frac{1}{2}x\ +8$  

• parallel

• perpendicular

• neither

Multiple Choice

Tell what the 2 equations are:

 $y=\frac{-7}{2}x+1\ \ \ \ and\ \ \ \ \ y=\frac{2}{7}x\ +8$  

• parallel

• perpendicular

• neither

Multiple Choice

Tell what the 2 equations are:

 $y=\frac{-8}{5}x-1\ \ \ \ and\ \ \ \ \ y=\frac{-5}{8}x\ +2$  

• parallel

• perpendicular

• neither

Multiple Choice

Tell what the 2 equations are:

 $-4x+9y=-1\ \ \ \ and\ \ \ \ \ -9x-4y=2$  

• parallel

• perpendicular

• neither

Solving for perpendicular lines when given an equation y=3x-8 and point

 $(-9,5)$  

• first-- pull the slope out of the equations

• second-- make the opposite reciprocal (change sign and flip)

• third-- plug into point slope form  $y-y=m\left(x-x\right)$  

• last-- solve for slope intercept

Multiple Choice

Solving for perpendicular lines when given an equation y=3x-8 and point (−9,5). What is the PERPENDICULAR slope that I would need to use to start solving this.

• $3$

• $-3$

• $\frac{-1}{3}$

• $\frac{1}{3}$

Hopefully you picked the slope of   $\frac{-1}{3}$  

• now plug that into your point slope form.

Multiple Choice

Solving for perpendicular lines when given an equation y=3x-8 and point $(-9,5)$  Which is the correct point slope form?

•  $y+5=\frac{-1}{3}\left(x-9\right)$  

•  $y-5=\frac{-1}{3}\left(x+9\right)$  

•  $y+5=\frac{-1}{3}\left(x+9\right)$  

•  $y-5=\frac{-1}{3}\left(x-9\right)$  

 $y-5=\frac{-1}{3}\left(x+9\right)$  

Hopefully you picked this one.  Now solve it for point slope form.

• Distribute into the () 

• add or subtract away form the y

Multiple Choice

Solving for perpendicular lines when given an equation y=3x-8 and point (−9,5)

• $y=\frac{-1}{3}x+8$

• $y=\frac{-1}{3}x-8$

• $y=\frac{-1}{3}x-2$

• $y=\frac{-1}{3}x+2$

Now you go and try on you own

link attached on moodle or just go to goformative.