Question

Write the equation in standard form for the line that passes through the points ( 4, -2 ) and ( 4, 8 )

Answer 1

@trish how do you write a line in standard form?

Answer 2

ax+by=c

Answer 3

Very good, correct. Hang on a minute.

Answer 4

So what happens if you entered the values for the first point in to the equation?

Answer 5

what numbers go where

Answer 6

Actually, there's a much easier way for you to figure out what's going on here. Take both points and plot them on http://www.desmos.com. Then draw a line through the points.

Answer 7

But putting the plots on the graph won't help get the answer

Answer 8

Yes, but it would show you something about the properties of the line created. You can draw the line through the points with your mind.

Answer 9

@trish

Answer 10

ok I did that

Answer 11

And what do you notice about the line? Does anything about it stand out to you?

Answer 12

they're parallel

Answer 13

@Hero

Answer 14

"They're" What do you mean? There is only ONE line.

Answer 15

oh ya

Answer 16

What you are supposed to observe is that the line created through points (4,8) and (4,-2) forms a vertical line. Has your lesson ever discussed the concept of a vertical line? Or is this your first time hearing of it?

Answer 17

I need to know the standard form

Answer 18

I know, however, the thing is, the general equation of the standard form of a line is Ax + By = C. But in this particular case, when the line is vertical, the slope is undefined. That nevertheless doesn't prevent us from being able to write the line in standard form.

Answer 19

@Hero so how do you write it

Answer 20

The easiest way to write it simply is to just know that the vertical line has the form
x = a, where a is the x coordinate of either point.

Answer 21

x=4?

Answer 22

Yes, correct. So basically, for vertical lines in standard form,
A = 1, B = 0, and C = a (the x coordinate of either point)