Asian Posted February 13, 2007 Share Posted February 13, 2007 Can someone explain to me why x^2=49, the value for x is plus or minus 7 Link to comment Share on other sites More sharing options...
timo Posted February 13, 2007 Share Posted February 13, 2007 Not sure what you mean. Both, +7 and -7 solve the equation: (+7)² = 49 and (-7)² = 49. Link to comment Share on other sites More sharing options...
psynapse Posted February 13, 2007 Share Posted February 13, 2007 Just in case the above isn't enough, remember a negative multiplied with a negative is a positive so there is no real way to know which set of numbers you get with roots. Link to comment Share on other sites More sharing options...
alan2here Posted February 13, 2007 Share Posted February 13, 2007 On a semi-related topic I once belived all of mathmatics was out by +1 because (n - 1) * (n + 1) = (n * n) + 1 Link to comment Share on other sites More sharing options...
the tree Posted February 13, 2007 Share Posted February 13, 2007 On a semi-related topic I once belived all of mathmatics was out by +1 because (n - 1) * (n + 1) = (n * n) + 1 When you were a child right?Well anyways, what you've written there doesn't seem to be right since the difference of two squares: [math]a^{2}-b^{2}=(a+b)(a-b)[/math] Link to comment Share on other sites More sharing options...
psynapse Posted February 13, 2007 Share Posted February 13, 2007 Nvm. It should be minus 1. good spot ^^ Link to comment Share on other sites More sharing options...
alan2here Posted February 14, 2007 Share Posted February 14, 2007 (4 - 1) * (4 + 1) = 15 4 * 4 = 16 (3 - 1) * (3 + 1) = 8 3 * 3 = 9 (7 - 1) * (7 + 1) = 48 3 * 3 = 49 My simple proff that my rule is right, and yes it was when I was a child I descovered it. Link to comment Share on other sites More sharing options...
Asian Posted February 14, 2007 Author Share Posted February 14, 2007 have u ever heard of difference of perfect ssquares? Link to comment Share on other sites More sharing options...
psynapse Posted February 14, 2007 Share Posted February 14, 2007 (n - 1) * (n + 1) = (n * n) + 1 Should read (n - 1) * (n + 1) = (n * n) - 1 Like your proof shows. Link to comment Share on other sites More sharing options...
Royston Posted February 15, 2007 Share Posted February 15, 2007 My simple proff that my rule is right,and yes it was when I was a child I descovered it. You're not expanding, that's why you're getting the incorrect result. You are familiar with expanding and the inverse...factorising ? Link to comment Share on other sites More sharing options...
alan2here Posted March 29, 2007 Share Posted March 29, 2007 lol, your right psynapse, the whole of mathmatics is off by -1 I guess. Whats "expanding" and "the inverse...factorising" and how does it make? (4 - 1) * (4 + 1) = 16and 4 * 4 = 16[/Code] Link to comment Share on other sites More sharing options...
ydoaPs Posted March 29, 2007 Share Posted March 29, 2007 (4*4)-1=15. you forgot the -1 part. Link to comment Share on other sites More sharing options...
alan2here Posted March 30, 2007 Share Posted March 30, 2007 (4 - 1) * (4 + 1) = 15 (4 * 4) - 1 = 15 4 * 4 = 16 There, still proves its all of by -1 Link to comment Share on other sites More sharing options...
Royston Posted March 30, 2007 Share Posted March 30, 2007 There, still proves its all of by -1 It doesn't prove maths is 'all' out by -1, because 4*4 and (4-1)(4+1) are not equivalent. Expanding is just...(4-1)(4+1) so 4*4=16, 4*1=4, 1*(-1)= -1, 4*-1= -4 16+4-1-4=15 So your results are right, but your reasoning to why the results are different is wrong. My first post was in response to your first calculation, sorry I missed the second. Link to comment Share on other sites More sharing options...
ydoaPs Posted March 30, 2007 Share Posted March 30, 2007 (4 - 1) * (4 + 1) = 15 (4 * 4) - 1 = 15 4 * 4 = 16 There, still proves its all of by -1 So, you can't understand why (n2-1)!=n2? I seriously don't see the problem here. (n+1)(n-1)=n2-1, not n2. Watch, I'll FOIL it for you. F(first terms multiplied together)+I(inside terms multiplied together)+O(outside terms multiplied together)+L(last terms multiplied together) (n+1)(n-1)=n2+(1)n+(-1)n+(1)(-1)=n2-1 Link to comment Share on other sites More sharing options...
alan2here Posted March 30, 2007 Share Posted March 30, 2007 ahh, I get it :¬) +1 * -1 is never going to be = to 0 Thats why (n-1)*(n+1) is not = to n*n Thanks :¬) now I understand. Link to comment Share on other sites More sharing options...
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