Question

Write the equation for the line shown below. (diagram in comments)

Answer 1

The answer to these 2 questions will help us get the equation.\
1. What is the y-intercept of that line?
2. What is the slope of that line?
Can you answer either of these?

Answer 2

is the slope 2?

Answer 3

No. For one thing, if the line is sloped downward from left-->right, the slope is negative. (the slope is not -2 either). We do know 2 points on the line, though. What 2 points do we know that are on the line?

Answer 4

4, -2

Answer 5

One point is obvious, one point is maybe not so obvious

Answer 6

yes. the other point is (0,0). Note that the line does go through (0,0). So now use the slope formula on those 2 points to get the slope. Do you remember how to do that?

Answer 7

whats the slope formula

Answer 8

very important formula in almost every topic of post-8th grade math:
Given 2 points: (x1,y1) and (x2,y2)
m=slope=(y2-y1) / (x2-x1)

Answer 9

-2 / 4

Answer 10

yes. and that simplifies to what fraction?

Answer 11

1/2

Answer 12

-1/2 .... don't forget the minus sign.

Answer 13

so than what would the equation be

Answer 14

Now, what is the y-intercept of that line? Do you know what a y-intercept is?

Answer 15

we're not ready to write the equation yet. we need to get the y-intercept

Answer 16

0,0

Answer 17

The y-intercept is just the value of y when the line crosses the y axis. Yes, that's right. For our purposes, the y-intercept is 0. y=0 when the line crosses the y axis

Answer 18

So, slope = -1/2....y-intercept is 0
What's the slope intercept equation of a line? Do you recall?

Answer 19

Again, very important concept:
slope intercept for:
y = mx + b
m is the slope , b is the y-intercept.
Plug in what we now know and you'll have the answer.

Answer 20

y= mx+b

Answer 21

yes

Answer 22

y=-1/2+0

Answer 23

you forgot about the x.
y = (-1/2)x + 0
and you can just leave off that 0 for the final answer
final answer y = (-1/2)x

Answer 24

ok thanks

Answer 25

sure. no problem