Page 1 of 2 1 2 LastLast
Results 1 to 10 of 14

Thread: Maths Help!!!

  1. #1

    Default Maths Help!!!

    Dd is subtracting negative numbers. We know that two negatives make a positive ie 3--1 is the same as 3+1. But I don't understand why ?!

    Can anyone either explain it to me or direct me somewhere with an explanation of 'why' ? Ta.

  2. Thank You Leaderboard
  3. #2
    Senior Member Arrived dbmamaz's Avatar
    Join Date
    Jun 2009
    Location
    VA
    Posts
    10,082
    Blog Entries
    7

    Default

    The best way I can explain it is probably looking at a number line. If you put a mark at 3 on the numberline, if you add 1 to it, you move 1 spot to the right, and land on 4. But if you had subtracted 1, you would move one spot to the left, and land on 2. If you add a negative number, that is the same as subtracting the same number, right? So if you add -1 to 3, instead of moving 1 spot to the right, you move one spot to the left. You do the opposite. Its the same thing w subtracting a negative, you do the opposite - subtracting a positive number, you move to the left, but subtracting a negative number, you move to the right.

    Another way to think of it is this. 3 - 2 is the same as 3 + {(-1)x(2)}. Does that make sense?

    So 3 - -2 is the same as 3 + {(-1)x(-2)}

    are you clear that -1x-2 = 2?

    You can also think of it as a balance beam. If i have 3 one-ounce disks on a scale, and I want to add a negative ounce, well, thats the same as taking an ounce away. The total weight will get smaller. If i want to take away the negative weight, i have to put that ounce back. Taking away a negative weight would make the total bigger. Ok, that might be the worst explanation yet!

    Better try khan academy - free and awesome videos starting w basic math.
    Cara, homeschooling one
    Raven, ds 10, all around intense kid
    Orion, floundering recent graduate
    22 yo dd, not at home
    Inactive blog at longsummer

  4. #3

    Default

    Actually, the balance beam explanation helps I can picture it so now I can hopefully explain it. I'll head on over to Khan academy too. Thanks!

  5. #4

    Default

    Maria Miller from Math Mammoth also has helpful videos on youtube you may want to check out.
    Sara

    Considering Homeschooling for my 2 monkeys
    • Monkey 1 5yr. in SK
    • Monkey 2 3yr. in JK

  6. #5
    Senior Member Arrived dbmamaz's Avatar
    Join Date
    Jun 2009
    Location
    VA
    Posts
    10,082
    Blog Entries
    7

    Default

    glad something i said made sense! I asked my husband, who has 4 math-related degrees, how he would explain the concept . . . he said he wouldnt. A lot of help that is!
    Cara, homeschooling one
    Raven, ds 10, all around intense kid
    Orion, floundering recent graduate
    22 yo dd, not at home
    Inactive blog at longsummer

  7. #6

    Default

    Well, the Khan academy vid was great at explaining how to do it but still not the why! I used the balance beam explanation to explain it to dd this morning and she said she got it.

  8. #7
    Senior Member Arrived dbmamaz's Avatar
    Join Date
    Jun 2009
    Location
    VA
    Posts
    10,082
    Blog Entries
    7

    Default

    Cool! Out of curiosity, I asked my 7 yo. He said everything is just opposite with negative numbers. So i guess thats not really a why.
    Cara, homeschooling one
    Raven, ds 10, all around intense kid
    Orion, floundering recent graduate
    22 yo dd, not at home
    Inactive blog at longsummer

  9. #8

    Default

    Saying it's opposite is sort of a why - if you look at a number line it's not the same, it's a mirror image, which is, indeed backwards.

    I also have trouble bending my head around negative numbers though. The why is really important though...
    Want to read about my homeschool?
    http://farrarwilliams.wordpress.com
    Children's Books, Homeschooling and Random Musings...

    Want help homeschooling or sending kids to college?
    http://simplify4you.com/

  10. #9

    Default

    I just don't like dd being able to do something but not able to articulate why, kwim ? That's how I ended up failing high school maths I like being able to have a picture rather than a numerical explanation for the 'why', which may be dumb, I don't know, I'm a maths failure! So 'mirror image' makes sense to me because I'm thinking of an Alice in Wonderland type thing where everything on that side of the mirror is opposite to what it is here, so of course two negatives will turn into positives...don't suppose there are any maths curriculums that um, explain things that way ?

    OK, with the little Alice story, dd is sure she's got it.
    Last edited by Stella M; 03-29-2011 at 09:57 PM.

  11. #10
    Senior Member Arrived dbmamaz's Avatar
    Join Date
    Jun 2009
    Location
    VA
    Posts
    10,082
    Blog Entries
    7

    Default

    actually there are a lot of math story books to explain ideas. I'm pretty sure there was one about negative numbers. You know, that living math site i'm always talking about . .. idk.

    But i think being able to picture it is important. I mean, at least being able to understand it past just the words that explain it. I found math easy until it got to things I couldnt picture . . . although my husband started trying to say something to our 7 yo about the rate at which speed is changing and somehow i remembered that that was calculus. I remembered it with enough confidence that I was able to say "You want to explain calculus to him?" and he looked positive for a moment and then faltered and said, "ok, maybe its too complicated." I'm usually so afraid of looking dumb in front of my husband i'm afraid to say anything about math. I'm always sure he thinks i'm explaining things wrong to the boys. but he's the only man i liked who wasnt intimidated by MY brain, so its a good thing overall.
    Last edited by dbmamaz; 03-29-2011 at 10:06 PM.
    Cara, homeschooling one
    Raven, ds 10, all around intense kid
    Orion, floundering recent graduate
    22 yo dd, not at home
    Inactive blog at longsummer

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
About us

SecularHomeschool.com was created to provide information, resources, and a place to share and connect with secular homeschoolers across the world. Secularhomeschool.com aims to be your one-stop shop for all things homeschool! We will be highlighting information about wonderful secular homeschool resources, and keeping you up to date with what is going on in the world of secular homeschooling. But that is only the beginning. SHS is your playground. A place to share the things that are important to you. A place to create and join groups that share your interests. A place to give and get advice. There are no limits to what you can do at Secular Homeschool, so join today and help build the community you have always wanted.

SecularHomeschool.com is a community and information source where secular homeschoolers ARE the majority. It is the home for non-religious homeschoolers, eclectic homeschoolers, freethinking homeschoolers AND anyone interested in homeschooling irrespective of religion. This site is an INCLUSIVE community that recognizes that homeschoolers choose secular homeschool materials and resources for a variety of reasons and to accomplish a variety of personal and educational goals. Although SecularHomeschool.com, and its members, have worked hard to compile a comprehensive directory of secular curricula, it does not attest that all materials advertised on our site, in our newsletters, or on our social media profiles are 100% secular. Rather, SecularHomeschool.com respects the aptitude of each individual homeschool parent to fully research any curriculum before acquiring it, to ensure that it holistically meets the educational, personal, and philosophical goals of each homeschooler.

Join us
Maths Help!!!