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### Course: 8th grade foundations (Eureka Math/EngageNY)>Unit 4

Lesson 1: Topic A: Foundations

# Intro to two-step equations

Here's how we solve a two step equation. It begins with the concept of equality: what we do to one side of the equation must be done to the other. Created by Sal Khan.

## Want to join the conversation?

• Do the rules of order of operations also count, but then in reverse?
So first you do:
3x + 2 = 14
3x = 12
x = 4

and not:

3x + 2 = 14
x + 2 = 4 6/9
x = 2 6/9
• You can change the order of operations. Your example has a flaw. You'll need to divide the 2 also by 3 on the left side.
3x + 2 = 14
x + 2/3 = 14/3
x = 12/3
x = 4
• Cant sal just / 3 (divide by three) than x 1/3 (multipy by 1/3)?
• Yes. Dividing by three is the exact same math as multiplying by 1/3.
• im in 2nd grade what am i learning
• Your future pain
• My teacher usually gives my class a challenge problem every week, each is supposed to be more challenging than the last, I was wondering how to solve for f(13)
f(x)=8x+g(9)-k(10)
g(1)=5+k(3)
k(1)=10-5x
2x=8
I think I know how to solve, but I'm not sure
• Does anyone see those two blocks he missed or is it just me?
And did he draw that scale? If he did props to him.
• I noticed, and yeah i agree, that scale is good
• Wouldn't it also work to think, 3*4=12, therefore, 3x=12 is the same thing as 3*4=12, leaving x=4?
• yes, that is basically what happens when you divide by the same number on both sides
• what if the x is on both sides
• I think that would make x basically any number. If the problem says the total weight on one side then you can find out what x is for example...

Lets say you have a scale and on the left side there are 6 kg (kilograms) blocks and 2 x blocks. On the right side you have 9 kg (kilograms) blocks and 1 x block. Each side has a total of 12 kg (kilograms).

What makes this problem possible is that the problem says the total weight on each side meaning x can't just be any number. Hopefully this helps someone and tell me what you think the answer is in the comments! :)
• I know this is very off topic, but I’ve tried to post questions and see comments in the Khan Academy app, but it doesn’t show up. Does anyone know to to see comments, or turn on the setting?
• When using the railroad track method, couldn't you just say:
3x +2 = 14
-2 = -2
3x = 12
/3 = /3
x = 4
Would that work instead of multiplying 1/3 of each side?