Use the linear pair postulate

[ErickaS]

I don’t think my math is right here. Can someone give me direction on this please?

 

[ErickaS]

I also got this...

 

[tkhunny]

View attachment 17475 I don’t think my math is right here. Can someone give me direction on this please?

Let's just ignore the second one. That makes no sense at all.

Start from 3x - 5 = 160 and try that again.

 

[ErickaS]

Let's just ignore the second one. That makes no sense at all.

Start from 3x - 5 = 160 and try that again.

X=55
3X-5=160
+5 +5
3X=165
/3 /3
X=55

 

[Dr.Peterson]

The important thing here is that what you do to each side must be done to all of each side, not just to part. So if you want to divide by three, you have to divide (3x - 5) by 3, not just divide 3x by 3 and leave the 5 alone.

Doing that would actually work, if you did it right; but it gets a little ugly, and most people who try it get it wrong. It's easier to deal with the addition or subtraction before you undo the multiplication, because of the way the order of operations works.

 

[pka]

don’t think my math is right here. Can someone give me direction on this please?

The concept of a linear pair postulate was first developed by Edwin Moise who was a R L Moore PhD student. His textbook is based upon Moore's axioms of basic geometry. I served as an assistant in two NSF high school level axiomatic geometry institutes based upon Moore's notes and directed by another one of Moore's students.
A linear pair postulate: Suppose that points \(A,~B,~\&~C\) are such that \(A-B-C\) and \(D \notin \overleftrightarrow {AB}\) then \(\angle ABD~\&~\angle DBC\) are a linear pair.
BTW: I never knew that degrees were ever use in these notes. We were always concerned with numbers.

 

[Steven G]

Here is a numerical example using your mistake.

We know that 15 + 6 = 21. I feel like dividing by 3.

I get 15/3 + 6 = 21/3 or 5+6 = 7 this is not true.

As Dr Peterson said you need to divide every term by 3 giving us

15/3 + 6/3 = 21/3 or 5 + 2 =7 which is correct.