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Calculate -56 – (-40) and check the commutative property under subtraction

 Apr 9, 2020
 #1
avatar+1955 
+1

This will be -56+40, which is -16

 

---Recheck---

 

Commutative Property: 40-56=-16

So, we know our work is correct!

 Apr 9, 2020
edited by CalTheGreat  Apr 9, 2020
edited by CalTheGreat  Apr 9, 2020
 #4
avatar+928 
+2

Using the commutative property, you would get (-40) - (-56)= (-40)+56= 16 proving that the commutative property does NOT work for subtraction.

 

🔥🔥🔥

 

Edit:

You didn't use the commutative property correctly...

HELPMEEEEEEEEEEEEE  Apr 9, 2020
edited by HELPMEEEEEEEEEEEEE  Apr 9, 2020
 #5
avatar+1955 
+2

Yeah, I need to flip the equation...

 

-56+40

=40-56

CalTheGreat  Apr 9, 2020
 #6
avatar+928 
+2

The two numbers are -56 and -40, when using a property you don't simplify -(-40) to 40 because that changes your proof.

 

🔥🔥🔥

 

Edit:

Based on what you're saying, one might confuse that you just proved that the commutative property works for subtraction when in fact it doesn't.

HELPMEEEEEEEEEEEEE  Apr 9, 2020
edited by HELPMEEEEEEEEEEEEE  Apr 9, 2020
 #7
avatar+1955 
+2

Oh... 

 

But I'm still not convinced about there being no solutions?

How about -(-40)-56

CalTheGreat  Apr 9, 2020
 #8
avatar+928 
+1

I'm not saying there are no solutions... You said

"Commutative Property: 40-56=-16

So, we know our work is correct!"

You can't use the commutative property to show that your work is correct for subtraction. 40-56= -16 is correct, but that isn't the commutative property which I think is the source of our confusion.

 

🔥🔥🔥

HELPMEEEEEEEEEEEEE  Apr 9, 2020
 #9
avatar+1955 
+2

Yeah. I say we get CPhill or someone.

 

I just looked at the check the commutative property under subtraction​ part of the question.

CalTheGreat  Apr 9, 2020
 #10
avatar+928 
+1

Let me clear this up... the commutative property is a+b=b+a this only works for addition and multiplication.

 

In the problem, we'll call -56, a, and -40, b. a-b= -56 - (-40)= -56+40= -16; b-a= -40 - (-56)= -40 + 56= 16. This shows that a-b does not equal b-a.

HELPMEEEEEEEEEEEEE  Apr 9, 2020
 #11
avatar+928 
+2

This might help.

HELPMEEEEEEEEEEEEE  Apr 9, 2020
 #12
avatar+1955 
+2

That's very true.

 

I wonder why the question said check it under subtraction...

CalTheGreat  Apr 9, 2020
 #13
avatar+928 
+1

This problem was meant to show the person that the commutative property doesn't work for subtraction. If they check it themselves then they would understand it better.

HELPMEEEEEEEEEEEEE  Apr 9, 2020
edited by HELPMEEEEEEEEEEEEE  Apr 9, 2020
 #14
avatar+1955 
+2

Oh, okay! Thanks for showing me.

 

Nice discussion!

CalTheGreat  Apr 9, 2020
 #15
avatar+928 
+1

Yeah! No problem...sorry if it seemed like I was being rude or anything...

 

🔥🔥🔥

HELPMEEEEEEEEEEEEE  Apr 9, 2020
 #16
avatar+1955 
+2

Of course not!

CalTheGreat  Apr 9, 2020
 #2
avatar+928 
+3

-56 - (-40)= -56+40= -16. The commutative property states that a+b=b+a. The commutative property does NOT work for subtraction because a-b doesn't equal b-a.

 

🔥🔥🔥

 Apr 9, 2020
 #3
avatar+1955 
+3

Check my solution. I think he means "recheck with it?"

CalTheGreat  Apr 9, 2020

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