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## Algebra 1

### Course: Algebra 1 > Unit 5

Lesson 6: Summary: Forms of two-variable linear equations# Forms of linear equations review

CCSS.Math: , ,

There are three major forms of linear equations: point-slope form, standard form, and slope-intercept form. We review all three in this article.

There are three main forms of linear equations.

Slope-intercept | Point-slope | Standard |
---|---|---|

y, equals, start color #ed5fa6, m, end color #ed5fa6, x, plus, start color #1fab54, b, end color #1fab54 | y, minus, start color #7854ab, y, start subscript, 1, end subscript, end color #7854ab, equals, start color #ed5fa6, m, end color #ed5fa6, left parenthesis, x, minus, start color #7854ab, x, start subscript, 1, end subscript, end color #7854ab, right parenthesis | A, x, plus, B, y, equals, C |

where start color #ed5fa6, m, end color #ed5fa6 is slope and start color #1fab54, b, end color #1fab54 is the y-intercept | where start color #ed5fa6, m, end color #ed5fa6 is slope and start color #7854ab, left parenthesis, x, start subscript, 1, end subscript, comma, y, start subscript, 1, end subscript, right parenthesis, end color #7854ab is a point on the line | where A, B, and C are constants |

## Example

A line passes through the points left parenthesis, minus, 2, comma, minus, 4, right parenthesis and left parenthesis, minus, 5, comma, 5, right parenthesis. Find the equation of the line in all three forms listed above.

Two of the forms require slope, so let's find that first.

Now we can plug in start color #ed5fa6, m, end color #ed5fa6 and one of the points, say start color #7854ab, left parenthesis, minus, 5, comma, 5, right parenthesis, end color #7854ab, to get

**point-slope form**, y, minus, start color #7854ab, y, start subscript, 1, end subscript, end color #7854ab, equals, start color #ed5fa6, m, end color #ed5fa6, left parenthesis, x, minus, start color #7854ab, x, start subscript, 1, end subscript, end color #7854ab, right parenthesis:Solving for y, we get

**slope-intercept form**, y, equals, start color #ed5fa6, m, end color #ed5fa6, x, plus, start color #1fab54, b, end color #1fab54:And adding 3, x to both sides, we get

**standard form, A, x, plus, B, y, equals, C:***Want another example? Check out this video.*

*Want to practice the different forms yourself? Check out this exercise.*

*Want a more in-depth review of each form? Check out these review articles:*

## Want to join the conversation?

- In the point slopes form, it looks like you're saying you could use either set of coordinates.I thought it was the first set of coordinates since it says x1 and y1. Please explain. Thanks.(14 votes)
- That is correct. You can definitely use either set of coordinates. Don't mix-and-match: you can't use x1 and y2, but you can use (x1, y1) or (x2, y2) and it will work just as well either way.(26 votes)

- How do you know when to use point slope form vs slope intercept form?(11 votes)
- Most of the time, it would be your choice. Though, your teacher may request that you use a specific approach to see if you know how to do it.(13 votes)

- when do you need to use slope?(11 votes)
- To determining the slope/ steepness of a line. You should review the slope videos if you need help.(2 votes)

- ax + by + c = 0

ax + by = c

I've heard of 2 "standard" forms of linear equations. Which one is correct?

should c in the 1st line be -c though? since im moving it from the right to left...?(6 votes)- hey! okay, so I'm pretty sure you're confusing a quadratic equation with a linear equation. A linear equation is a straight line, while a quadratic is a curve/parabola. You'll probably learn that later in algebra 1 and 2.

anyways, the standard linear equation is ax+by=c, while the standard quadratic equation is slightly different from what you have; it should be ax^2+bx+c=0

hope this helps!!(12 votes)

- Why are point-slope operations the opposite?

For example, the point is (2,-3).

why is y+3=3/4(x-2) correct but not y-3=3/4(x+2)?(4 votes)- Point slope form is a variation of the slope formula:

Slope m = (y2-y1)/(x2-x1)

If you mulitply both sides by (x2-x1), then you get point slope form:

(y2-y1) = m(x2-x1)

Then, they swab a couple of variables to clarify the variables that stay. X2 becomes X, and Y2 becomes Y. And, you have the point slope form.

Remember, slope is calculated as the change in Y over the change in X. So, it requires the subtraction.

Hope this helps.(7 votes)

- i must be behind in math because all of this is way too confusing(7 votes)
- what’s point-slope form going to be useful for?(4 votes)
- Point slope form is important because it can give us another set of coordinate pairs when we are only given one. Using algebraic manipulation, you can find coordinates
*and*the slope from just that equation which helps with graphing. Being able to readily switch from different linear equation forms helps solving complex problems. Hope this helps. 🙃(6 votes)

- at the end it says this is a standard form y+3x=−10

it sould be fist 3x +y= -10 isn't ?(4 votes)- Specifically there are a lot of teachers that would mark y+3x=−10 wrong. Maybe correctly; the form is the whole point of the exercise.(2 votes)

- Is it possible to convert standard form back to point-slope directly?(4 votes)
- What happens when you have these coordinates (2,7) (6,7) and my slope ends up with 0/4, is this possible?(3 votes)
- Yes! It is possible! if you end up with a slope of 0 or a fraction with zero as the numerator, that's known as a zero slope. On a graph, it looks like a horizontal line. Hope this helps!(5 votes)