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### Course: Algebra (all content)>Unit 3

Lesson 1: Two-variable linear equations intro

# Solutions to 2-variable equations: graphical (old)

An old video of Sal checking whether (3,-4) is a solution of 5x+2y=7 by graphing the equation and checking if (3,-4) is on the line. Created by Sal Khan.

## Want to join the conversation?

• How did you come out with 3.5?
• He chooses an x value and substitutes it into the equation. Using that x value, he solves for y. So, `5x + 2y = 7` where x = 0 gives you the equation `5・0 + 2y = 7`.

5 times 0 is 0, so simplifying the equation gives you `2y = 7`.
We need to solve for y, so we divide both sides by 2. `2y / 2 = 7 / 2`
2y divided by 2 is just `y`.
7 divided by 2 is `3.5`.
Therefore, the final equation is `y = 3.5`.

Hope that helps! :)
• We just started this subject in math today. The teacher explained the process to us and I didn't really understand it. I just watched the viedo and I still don't understand it. Could you explain it to me plz? thank you! =)
• All you are doing is replacing x and y with their respective values and solving it.
• How does drawing the line on the graph prove that 3,-4 are the solution to 5x+2y=7?
• The line is the line of the equation 5x+2y=7. If (3,-4) co-ordinate falls on that line, then it is a solution of the equation.
• ordered pair solutions for x=0
• what is 2x-8y=8
• Would (2, -5) be a solution to 4 + 3x = -2y? When Sal does the equations like the one in this video I am able to understand it, but when the y value is to the right of the equal sign, I am not sure how to do it correctly.
• The equation is no different when the y is on the right side of the equation. If you are not understanding the equation while it is in this form, you can flip the equation so y is on the left side. Hope this helps you get the correct answer for the equation.
• is -4,5 a solution of y =2x-4
• What is the purpose for graphs when you have equations?
• i think it is so the teachers can see if u understand the problem