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## Algebra 1

### Unit 5: Lesson 3

Writing slope-intercept equations- Slope-intercept equation from graph
- Writing slope-intercept equations
- Slope-intercept equation from graph
- Slope-intercept equation from slope & point
- Slope-intercept equation from two points
- Slope-intercept from two points
- Constructing linear equations from context
- Writing linear equations word problems
- Slope-intercept form review

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# Slope-intercept form review

Review slope-intercept form and how to use it to solve problems.

## What is slope-intercept form?

Slope-intercept is a specific form of linear equations in two variables:

When an equation is written in this form, start color #ed5fa6, m, end color #ed5fa6 gives the slope of the line and start color #1fab54, b, end color #1fab54 gives its y-intercept.

*Want to learn more about slope-intercept form? Check out this video.*

## Finding slope-intercept equation from features or graph

### Example 1: Equation from slope and intercept

Suppose we want to find the equation of the line whose slope is start color #ed5fa6, minus, 1, end color #ed5fa6 and y-intercept is left parenthesis, 0, comma, start color #1fab54, 5, end color #1fab54, right parenthesis. Well, we simply plug start color #ed5fa6, m, equals, minus, 1, end color #ed5fa6 and start color #1fab54, b, equals, 5, end color #1fab54 into slope-intercept form!

### Example 2: Equation from two points

Suppose we want to find the line that passes through the points left parenthesis, 0, comma, minus, 4, right parenthesis and left parenthesis, 3, comma, minus, 1, right parenthesis. First, we notice that left parenthesis, 0, comma, start color #1fab54, minus, 4, end color #1fab54, right parenthesis is the y-intercept. Second, we use the two points to find the slope:

Now we can write the equation in slope-intercept:

*Want to try more problems like this? Check out these exercises:*

## Finding features and graph from slope-intercept equation

When we have a linear equation in slope-intercept form, we can quickly find the slope and y-intercept of the corresponding line. This also allows us to graph it.

Consider, for example, the equation y, equals, start color #ed5fa6, 2, end color #ed5fa6, x, start color #1fab54, plus, 3, end color #1fab54. We can quickly tell that the corresponding line has a slope of start color #ed5fa6, 2, end color #ed5fa6 and its y-intercept is left parenthesis, 0, comma, start color #1fab54, 3, end color #1fab54, right parenthesis. Now we can graph the line:

*Want to try more problems like this? Check out these exercises:*

## Want to join the conversation?

- i dont know how to find slope(2 votes)
- pay attention to this review and write everything down the you will prob. get bro(3 votes)

- how can i graph lines without having the y intercept on the graph?(2 votes)
- You can graph any line from its equation by finding and graphing any 2 points that satisfy the equation.

Alternatively, if you know the slope and any point on the line you can graph the point and use the slope to find more points on the line.

You can find more details in the lessons at this link: https://www.khanacademy.org/math/algebra/two-var-linear-equations(4 votes)

- This has no use in the real world.(2 votes)
- Slope? It can be used later to calculate really important things.(4 votes)

- how do you find the slope(3 votes)
- Here's my explanation :)

The**slope of the line**is another way of saying**How steep is this line**?

To find an exact number for that, we use the concept**rise over run**.

First, you find two points on the line,*(Let's say our points are (3,3) and (4,5))*

Next you find out how much the line**runs**, aka how much it goes sideways within the two points we picked. To do that, you take the point with the greatest x value, and subtract the x value of the other point:

4-3=1

Now let's find the**rise**aka how much the line goes up within the two points we picked. To do that, we take the y value of our first point, and subtract the y value of our second point:

5-3=2

Now we have our**Rise***(2)*and our**Run***(1)*, so let's put**Rise over Run**:

2/1**simplify**

2

And we have the slope of the line!(1 vote)

- I still don't know how to graph, this is so hard... :((2 votes)
- y=mx+b

y=y

m=any number

x=x

b=any number

b is the y intercept, which is when x is zero what y is.

Did this help? Or do you not understand how to graph from a slope intercept form?(4 votes)

- how do you figure out how to point it(2 votes)
- Please clarify your question... what do you mean by "how to point it"?(0 votes)

- how do I find the y intercept of the line with the equation 4x-5y+15=0? I'm so lost!(0 votes)
- The y-intercept is the point on the y-axis where the line crosses the y-axis. This means the x-coordinate for that point =0. Thus, you can always find the y-intercept by setting x=0 in the equation and solving for "y".

4(0) - 5y + 15 = 0

-5y + 15 = 0

15 = 5y

3 = y

Your y-intercept is at: (0, 3)

Hope this helps..(4 votes)

- why is this so hard? :((2 votes)
- It’s okay. I really struggled with this at first. Just rewatch videos, do a lot of practice problems, etc. and you’ll get the hang of it!(0 votes)

- If the slope of a line, for example is 2/1, I understand that the slope is 2. But what do I do if the slope is something like 3/4 or 5/8?(1 vote)
- It is quite common for slopes to be fractions.

A slope of 3/4 tells you that the line goes up 3 units as it moves right 4 units.

Similarly, a slope of 5/8 tells you that the line goes up 5 units as it moves 8 units to the right.

Hope this helps.(2 votes)

- Here is the problem A line having a slope of 3/4 passes through the point (-8,4). Write the equation of this line as y=mx+b

This is what i have y=3/4x + b

4=-96/4 +b(1 vote)- Yup, you've got everything correct. Now what's left is for you to solve for b and afterwards replace the b in your y = 3/4x + b. I hope this helped!(2 votes)