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  3. Proof for 1=2 (Identify the error in this proof)

Proof for 1=2 (Identify the error in this proof)

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  • L Offline
    L Offline
    Lost User
    wrote on last edited by
    #1

    Now 1 = 1 LHS = RHS 2+2 = 2^2 = 4 3+3+3 = 3^2 = 9 4+4+4+4 = 4^2 = 16 Thus by mathematical induction we can say, x+x+x+x......(x times) = x^2 Differentiating LHS and RHS with respect to x d/dx (x) =1 and d/dx (x^2) = 2x So we get, 1+1+1+1......(x times) = 2x 1 added 'x' times equals to x. ( 1 added 3 times equals 3, and so on) => x = 2x Thus, 1 = 2 So, what's wrong in this??? :-D

    C S L 7 Replies Last reply
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    • L Lost User

      Now 1 = 1 LHS = RHS 2+2 = 2^2 = 4 3+3+3 = 3^2 = 9 4+4+4+4 = 4^2 = 16 Thus by mathematical induction we can say, x+x+x+x......(x times) = x^2 Differentiating LHS and RHS with respect to x d/dx (x) =1 and d/dx (x^2) = 2x So we get, 1+1+1+1......(x times) = 2x 1 added 'x' times equals to x. ( 1 added 3 times equals 3, and so on) => x = 2x Thus, 1 = 2 So, what's wrong in this??? :-D

      C Offline
      C Offline
      Chris Maunder
      wrote on last edited by
      #2

      d/dx (x + ... + x) != 1 + ... + 1 (x times), since the number of x's depends on x itself.

      d/dx (x + ... + x) = d/dx (x (1 + ... + 1))
      = d/dx ( x.x )
      = x

      cheers, Chris Maunder

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      • L Lost User

        Now 1 = 1 LHS = RHS 2+2 = 2^2 = 4 3+3+3 = 3^2 = 9 4+4+4+4 = 4^2 = 16 Thus by mathematical induction we can say, x+x+x+x......(x times) = x^2 Differentiating LHS and RHS with respect to x d/dx (x) =1 and d/dx (x^2) = 2x So we get, 1+1+1+1......(x times) = 2x 1 added 'x' times equals to x. ( 1 added 3 times equals 3, and so on) => x = 2x Thus, 1 = 2 So, what's wrong in this??? :-D

        S Offline
        S Offline
        Slavo Furman
        wrote on last edited by
        #3

        Hello! We can say that '1 = 1', '2+2 = 4', '3+3+3 = 3^2', etc. is true. But it is clear that 'x+x+x+x......(x times) = x^2' is simply not true for 'x' values where x < 0, so 'x+x+x+x......(x times) = x^2' is not true in general. SlavoF "I hear and I forget. I see and I remember. I do and I understand." --Confucius

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        • L Lost User

          Now 1 = 1 LHS = RHS 2+2 = 2^2 = 4 3+3+3 = 3^2 = 9 4+4+4+4 = 4^2 = 16 Thus by mathematical induction we can say, x+x+x+x......(x times) = x^2 Differentiating LHS and RHS with respect to x d/dx (x) =1 and d/dx (x^2) = 2x So we get, 1+1+1+1......(x times) = 2x 1 added 'x' times equals to x. ( 1 added 3 times equals 3, and so on) => x = 2x Thus, 1 = 2 So, what's wrong in this??? :-D

          L Offline
          L Offline
          Lost User
          wrote on last edited by
          #4

          x+x+x+x+ ... = nx ; not x+x+x+x+ ... = x^2; d/dx 1+1+1+1+ ... = n Which is ok. I'am not sure, but you are probably mixing x's in an incompatible manner. Somehow. Anyway, I am not a math expert.

          J 1 Reply Last reply
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          • L Lost User

            Now 1 = 1 LHS = RHS 2+2 = 2^2 = 4 3+3+3 = 3^2 = 9 4+4+4+4 = 4^2 = 16 Thus by mathematical induction we can say, x+x+x+x......(x times) = x^2 Differentiating LHS and RHS with respect to x d/dx (x) =1 and d/dx (x^2) = 2x So we get, 1+1+1+1......(x times) = 2x 1 added 'x' times equals to x. ( 1 added 3 times equals 3, and so on) => x = 2x Thus, 1 = 2 So, what's wrong in this??? :-D

            L Offline
            L Offline
            Lost User
            wrote on last edited by
            #5

            First all you're really doing is showing x * x = x ^ 2. x + x + ... { x times } = x ^ 2 => x * ( 1 + 1 + ...) = x ^ 2 {with 1 added x times } this is, x * ( x ) = x ^ 2 so d/dx of this is 1x + x1 = 2x => 2x = 2x, or x = x { or 2 = 2, if you want, as long as x<>0 } { d/dx (uv) = du/dx * v + u * dv/dx }. It seems that your error was in assuming d/dx ( x + x + ...) { x times } = x :-D

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            • L Lost User

              Now 1 = 1 LHS = RHS 2+2 = 2^2 = 4 3+3+3 = 3^2 = 9 4+4+4+4 = 4^2 = 16 Thus by mathematical induction we can say, x+x+x+x......(x times) = x^2 Differentiating LHS and RHS with respect to x d/dx (x) =1 and d/dx (x^2) = 2x So we get, 1+1+1+1......(x times) = 2x 1 added 'x' times equals to x. ( 1 added 3 times equals 3, and so on) => x = 2x Thus, 1 = 2 So, what's wrong in this??? :-D

              L Offline
              L Offline
              Lost User
              wrote on last edited by
              #6

              You can't defferenciate one side as a whole and the other in pieces. Doh !! :eek: Another example: 1^2 + 1^2 + 1^2 + 1^2 != (1+1+1+1)^2 You cannot square each bit as an individual !!!!

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              • L Lost User

                Now 1 = 1 LHS = RHS 2+2 = 2^2 = 4 3+3+3 = 3^2 = 9 4+4+4+4 = 4^2 = 16 Thus by mathematical induction we can say, x+x+x+x......(x times) = x^2 Differentiating LHS and RHS with respect to x d/dx (x) =1 and d/dx (x^2) = 2x So we get, 1+1+1+1......(x times) = 2x 1 added 'x' times equals to x. ( 1 added 3 times equals 3, and so on) => x = 2x Thus, 1 = 2 So, what's wrong in this??? :-D

                L Offline
                L Offline
                Lost User
                wrote on last edited by
                #7

                > d/dx (x) =1 and d/dx (x^2) = 2x What is this crap? D / DX * (X) = 1 // true D / DX * (X^2) != 2x // you dolt... D / DX * (X^2) = D / DX * X * X = 1 / X * X * X = (X * X) / X ... ergo equals X not 2x > 1 added 'x' times equals to x. ( 1 added 3 times equals 3, and so on) > => x = 2x 1 added X times = X * 1... 1 * X = X x = x 1 = 1 > Thus, 1 = 2 Thus 1 != 2 , 1 = 1 ===== Peace in the middle east. No><

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                • L Lost User

                  Now 1 = 1 LHS = RHS 2+2 = 2^2 = 4 3+3+3 = 3^2 = 9 4+4+4+4 = 4^2 = 16 Thus by mathematical induction we can say, x+x+x+x......(x times) = x^2 Differentiating LHS and RHS with respect to x d/dx (x) =1 and d/dx (x^2) = 2x So we get, 1+1+1+1......(x times) = 2x 1 added 'x' times equals to x. ( 1 added 3 times equals 3, and so on) => x = 2x Thus, 1 = 2 So, what's wrong in this??? :-D

                  L Offline
                  L Offline
                  Lost User
                  wrote on last edited by
                  #8

                  The most basic mistake is differentiating while this is forbidden/useless here. Your induction proof is for natural numbers only, while differentialing is done over the real or complex numbers. The entire theory of differentition is built upon limit theorems which exist over the real numbers, but not over the natural numbers. Next mistake (ignoring the first) is treating x once as a constant and once as a variable. P.S. The most interesting false proofs of this kind come from integration theory, there mistakes are much harder to find. Felix.

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                  • L Lost User

                    x+x+x+x+ ... = nx ; not x+x+x+x+ ... = x^2; d/dx 1+1+1+1+ ... = n Which is ok. I'am not sure, but you are probably mixing x's in an incompatible manner. Somehow. Anyway, I am not a math expert.

                    J Offline
                    J Offline
                    Jason Douglas
                    wrote on last edited by
                    #9

                    The way you've shown it (nx) is correct, except that you're forgetting that n = x in each case. I've seen this proven one other way (although I forget the exact steps), and it involved division by 0. The next proof was to show that the Earth is flat... Why do we waste our time with these things? :)

                    L 1 Reply Last reply
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                    • J Jason Douglas

                      The way you've shown it (nx) is correct, except that you're forgetting that n = x in each case. I've seen this proven one other way (although I forget the exact steps), and it involved division by 0. The next proof was to show that the Earth is flat... Why do we waste our time with these things? :)

                      L Offline
                      L Offline
                      Lost User
                      wrote on last edited by
                      #10

                      Well, that's exactly the problem. It's true that 'x=n' in each case. But, strictly speaking can we write that down and perform derivation based on that assumption? Those variables are essentialy different. I am not sure, but it looks strange to me. Given the number of people involved in this 'math-like games', it appears that MFC programmers are quite idle falks, despite 50+ working hours/week.

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                      • S Slavo Furman

                        Hello! We can say that '1 = 1', '2+2 = 4', '3+3+3 = 3^2', etc. is true. But it is clear that 'x+x+x+x......(x times) = x^2' is simply not true for 'x' values where x < 0, so 'x+x+x+x......(x times) = x^2' is not true in general. SlavoF "I hear and I forget. I see and I remember. I do and I understand." --Confucius

                        L Offline
                        L Offline
                        Lost User
                        wrote on last edited by
                        #11

                        Slavo you were very close.... The function f(x)= x+x+x+x.....(X times) = x^2 is true only for x>0 and absolute values of x. It fails between value x=1 and x=2. Thus, since this function f(x) is not continuous, it is not even differentiable, even for a limiting case. ;) Debanjan

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