Please explain this simple equation: 5=9 -2x

A

AdultLearningMathAgain

New member
Joined
Jan 16, 2022
Messages
4
Hello Everyone!

The equation is a simple one but I don't understand the "why" of it.

[math]5=9 -2x[/math]
The way I tried to solve it was I first targetted the "9" and did a -9 on both sides, but according to the book, I should have done a -2x instead.

When I see an equation like above, I usually target the "free number" first before going for the x, so I'm confused.

Thanks!
 
I cannot comment on the book's suggestion, but what do you get when you use your approach ?
 
AdultLearningMathAgain said:
Hello Everyone!

The equation is a simple one but I don't understand the "why" of it.

[math]5=9 -2x[/math]
The way I tried to solve it was I first targetted the "9" and did a -9 on both sides, but according to the book, I should have done a -2x instead.

When I see an equation like above, I usually target the "free number" first before going for the x, so I'm confused.

Thanks!
Click to expand...
Your method of eliminating '9' first is valid.

It is just two different ways to get to the same results.
 
AdultLearningMathAgain said:
At the end I get -4 divided by 2, which is -2, yes?

I am trying to write the equation here but it 's not working too good for me :(
Click to expand...
[math]5=9-2x\\ 5 + \blue{-9}=9-\blue{9} -2x \quad \text{subtract 9 on both sides}\\ \frac{-4}{\blue{2}}=\frac{-2x}{\blue{2}} \quad \text{ divide both sides by 2}\\ -2=\red{-}x[/math]This is what you arrived so far. Notice you have [imath]-x[/imath], not x. Need one more step to get the final answer.
 
BigBeachBananas said:
[math]5=9-2x\\ 5 + \blue{-9}=9-\blue{9} -2x \quad \text{subtract 9 on both sides}\\ \frac{-4}{\blue{2}}=\frac{-2x}{\blue{2}} \quad \text{ divide both sides by 2}\\ -2=-x[/math]This is what you arrived so far. Notice you have [imath]-x[/imath], not x. Need one more step to solve get the final answer.
Click to expand...
I'm struggling to get the hang of writing the way you did, till then, here is a (crappy) picture that I hope will work.

https://imgur.com/a/NsrYyhT
 
Notice that on the right hand side, when you cancel the 2s, you are left with -x not x.
That is you should have -2 = -x leading to x=2.
You have just ignored the -ve sign on the RHS.
 
5 = 9 - 2x

I don' think that you should do things so mechanically.
2x is unknown, so call it what

Now 5 = 9 - 2x becomes 5 = 9 - what. I hope you see that the what becomes 4 (since 5 = 9 - 4)

So 2x=4. 2 times what equals 4---- 2x2 = 4
So x=2.

Just use common sense logic.
 
You must log in or register to reply here.
Top