document.write( "Question 167734: i have some problems with this system ? can you tell me how to solution sytem\r
\n" ); document.write( "\n" ); document.write( "sytem is x^3 + y^3 = 1
\n" ); document.write( " x^2y + 2xy^2 + Y^3 = 2\r
\n" ); document.write( "\n" ); document.write( "please contact with me as soon as you can
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Algebra.Com's Answer #123725 by Edwin McCravy(20054)\"\" \"About 
You can put this solution on YOUR website!
\"system%28x%5E3%2By%5E3=1%2C+x%5E2y%2B2xy%5E2%2By%5E3=2%29\"
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document.write( "Let \"y=kx\"\r\n" );
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document.write( "Now we can solve each for \"x%5E3\" as long as we require that\r\n" );
document.write( "\"1%2Bk%5E3%3C%3E0\" and \"k%2B2k%5E2%2Bk%5E3%3C%3E0\"\r\n" );
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document.write( "So we will take Case 1 as when they are both true:\r\n" );
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document.write( "Case 1:  \"1%2Bk%5E3%3C%3E0\" and \"k%2B2k%5E2%2Bk%5E3%3C%3E0\"\r\n" );
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document.write( "Then we can solve both for \"x%5E3\" without\r\n" );
document.write( "dividing by 0:\r\n" );
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document.write( "\"system%28x%5E3=1%2F%281%2Bk%5E3%29%2C+x%5E3=2%2F%28k%2B2k%5E2%2Bk%5E3%29%29\"\r\n" );
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document.write( "Since the left sides are equal, so are the right \r\n" );
document.write( "sides:\r\n" );
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document.write( "\"1%2F%281%2Bk%5E3%29=2%2F%28k%2B2k%5E2%2Bk%5E3%29\"\r\n" );
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document.write( "Cross multiply:\r\n" );
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document.write( "\"2%281%2Bk%5E3%29=1%28k%2B2k%5E2%2Bk%5E3%29\"\r\n" );
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document.write( "\"2%2B2k%5E3=k%2B2k%5E2%2Bk%5E3\"\r\n" );
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document.write( "Get 0 on the right and left side in descending\r\n" );
document.write( "order:\r\n" );
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document.write( "\"k%5E3-2k%5E2-k%2B2=0\"\r\n" );
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document.write( "Factor k^2 out of the first two terms on the left,\r\n" );
document.write( "and factor -1 out of the last two terms on the left:\r\n" );
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document.write( "\"k%5E2%28k-2%29-1%28k-2%29=0\"\r\n" );
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document.write( "Factor \"k-2%29\" out of both terms on the left:\r\n" );
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document.write( "\"%28k-2%29%28k%5E2-1%29=0\"\r\n" );
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document.write( "Factor the second parentheses on the left:\r\n" );
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document.write( "\"%28k-2%29%28k-1%29%28k%2B1%29=0\"\r\n" );
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document.write( "Using the zero-factor principle:\r\n" );
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document.write( "Remember that the requirements for Case 1 were:\r\n" );
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document.write( "\"1%2Bk%5E3%3C%3E0\" and \"k%2B2k%5E2%2Bk%5E3%3C%3E0\"\r\n" );
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document.write( "We investigate to see whether \"k=2\" satisfies\r\n" );
document.write( "both of those requirements. Substituting,\r\n" );
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document.write( "\"1%2Bk%5E3%3C%3E0\" and \"k%2B2k%5E2%2Bk%5E3%3C%3E0\"\r\n" );
document.write( "\"1%2B2%5E3%3C%3E0\" and \"2%2B2%282%29%5E2%2B%282%29%5E3%3C%3E0\"\r\n" );
document.write( "\"1%2B8%3C%3E0\" and \"2%2B2%284%29%2B8%3C%3E0\"\r\n" );
document.write( "\"9%3C%3E0\" and \"2%2B8%2B8%3C%3E0\"\r\n" );
document.write( "\"9%3C%3E0\" and \"18%3C%3E0\"\r\n" );
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document.write( "So there are both satisfied, so we can use \"k=2\"\r\n" );
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document.write( "We now investigate to see whether \"k=1\" satisfies\r\n" );
document.write( "both of those requirements. Substituting,\r\n" );
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document.write( "\"1%2Bk%5E3%3C%3E0\" and \"k%2B2k%5E2%2Bk%5E3%3C%3E0\"\r\n" );
document.write( "\"1%2B1%5E3%3C%3E0\" and \"2%2B2%281%29%5E2%2B%281%29%5E3%3C%3E0\"\r\n" );
document.write( "\"1%2B1%3C%3E0\" and \"2%2B2%281%29%2B1%3C%3E0\"\r\n" );
document.write( "\"2%3C%3E0\" and \"2%2B2%2B1%3C%3E0\"\r\n" );
document.write( "\"2%3C%3E0\" and \"5%3C%3E0\"\r\n" );
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document.write( "So these are both satisfied, so we can also use \"k=1\"\r\n" );
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document.write( "We now investigate to see whether \"k=-1\" satisfies\r\n" );
document.write( "both of those requirements. Substituting,\r\n" );
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document.write( "\"1%2Bk%5E3%3C%3E0\" and \"k%2B2k%5E2%2Bk%5E3%3C%3E0\"\r\n" );
document.write( "\"1%2B%28-1%29%5E3%3C%3E0\" and \"2%2B2%28-1%29%5E2%2B%28-1%29%5E3%3C%3E0\"\r\n" );
document.write( "\"1-1%3C%3E0\" and \"2%2B2%281%29-1%3C%3E0\"\r\n" );
document.write( "\"0%3C%3E0\" and \"2%2B2-1%3C%3E0\"\r\n" );
document.write( "\"0%3C%3E0\" and \"3%3C%3E0\"\r\n" );
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document.write( "Since the first is not satisfied we cannot use \"k=-1\"\r\n" );
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document.write( "Now we use\"k=1\" and since \"y=kx\", \"y=x\" in the original:\r\n" );
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document.write( "\"system%28x%5E3%2By%5E3=1%2C+x%5E2y%2B2xy%5E2%2By%5E3=2%29\"\r\n" );
document.write( "\"system%28x%5E3%2Bx%5E3=1%2C+x%5E2x%2B2xx%5E2%2Bx%5E3=2%29\"\r\n" );
document.write( "\"system%282x%5E3=1%2C+x%5E3%2B2x%5E3%2Bx%5E3=2%29\"\r\n" );
document.write( "\"system%282x%5E3=1%2C+4x%5E3=2%29\"\r\n" );
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document.write( "solving both for \"x%5E3\"\r\n" );
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document.write( "\"system%28x%5E3=1%2F2%2Cx%5E3=1%2F2%29\"\r\n" );
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document.write( "So these are the same, so we can\r\n" );
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document.write( "get the real solution by taking cube roots\r\n" );
document.write( "of both sides:\r\n" );
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document.write( "\"x=root%283%2C1%2F2%29\"\r\n" );
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document.write( "rationalizing:\r\n" );
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document.write( "\"x=root%283%2C%281%2A4%29%2F%282%2A4%29%29+\"\r\n" );
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document.write( "\"x=root%283%2C4%2F8%29\"\r\n" );
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document.write( "\"x=root%283%2C4%29%2F2%29\"\r\n" );
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document.write( "And since in this case \"y=x\"\r\n" );
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document.write( "we have solution\r\n" );
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document.write( "But that's not necessarily the only solution.\r\n" );
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document.write( "Now we use\"k=2\" and since \"y=kx\", \"y=2x\" in the original:\r\n" );
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document.write( "\"system%28x%5E3%2By%5E3=1%2C+x%5E2y%2B2xy%5E2%2By%5E3=2%29\"\r\n" );
document.write( "\"system%28x%5E3%2B%282x%29%5E3=1%2C+x%5E2%282x%29%2B2x%282x%29%5E2%2B%282x%29%5E3=2%29\"\r\n" );
document.write( "\"system%28x%5E3%2B8x%5E3=1%2C+2x%5E3%2B2x%284x%5E2%29%2B8x%5E3=2%29\"\r\n" );
document.write( "\"system%289x%5E3=1%2C+2x%5E3%2B8x%5E3%2B8x%5E3=2%29\"\r\n" );
document.write( "\"system%289x%5E3=1%2C+18x%5E3=2%29\"\r\n" );
document.write( "\"system%289x%5E3=1%2C+9x%5E3=1%29\"\r\n" );
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document.write( "solving both for \"x%5E3\"\r\n" );
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document.write( "\"system%28x%5E3=1%2F9%2Cx%5E3=1%2F9%29\"\r\n" );
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document.write( "So these are the same, so we can\r\n" );
document.write( "get a real solution by taking cube roots\r\n" );
document.write( "of both sides:\r\n" );
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document.write( "\"x=root%283%2C1%2F9%29\"\r\n" );
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document.write( "rationalizing:\r\n" );
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document.write( "\"x=root%283%2C%281%2A3%29%2F%289%2A3%29%29+\"\r\n" );
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document.write( "\"x=root%283%2C3%2F27%29\"\r\n" );
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document.write( "\"x=root%283%2C3%29%2F3%29\"\r\n" );
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document.write( "And since in this case \"y=2x\"\r\n" );
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document.write( "we have solution\r\n" );
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document.write( "So we have found two solutions.  But this\r\n" );
document.write( "was only for Case 1, when \r\n" );
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document.write( "\"1%2Bk%5E3%3C%3E0\" and \"k%2B2k%5E2%2Bk%5E3%3C%3E0\"\r\n" );
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document.write( "We must investigate the possibility of\r\n" );
document.write( "solutions when one or both of these are\r\n" );
document.write( "violated:\r\n" );
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document.write( "Case 2: \"1%2Bk%5E3=0\"\r\n" );
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document.write( "This means that\r\n" );
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document.write( "\"k%5E3=-1\" or \"k=-1\"\r\n" );
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document.write( "Now we use\"k=-1\" and since \"y=kx\", \"y=-x\" in the original:\r\n" );
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document.write( "\"system%28x%5E3%2By%5E3=1%2C+x%5E2y%2B2xy%5E2%2By%5E3=2%29\"\r\n" );
document.write( "\"system%28x%5E3%2B%28-x%29%5E3=1%2C+x%5E2%28-x%29%2B2x%28-x%29%5E2%2B%28-x%29%5E3=2%29\"\r\n" );
document.write( "\"system%28x%5E3-x%5E3=1%2C+-x%5E3%2B2x%5E3-x%5E3=2%29\"\r\n" );
document.write( "\"system%280=1%2C+0=2%29\"\r\n" );
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document.write( "This is certainly not true, so Case 2\r\n" );
document.write( "\"1%2Bk%5E3=0\" is not possible since it produces\r\n" );
document.write( "no solutions.\r\n" );
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document.write( "Case 3: \"k%2B2k%5E2%2Bk%5E3=0\"\r\n" );
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document.write( "Factoring out k on the left:\r\n" );
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document.write( "\"k%281%2B2k%2Bk%5E2%29=0\"\r\n" );
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document.write( "Factoring the trinomial in parenheses:\r\n" );
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document.write( "\"k%281%2Bk%29%281%2Bk%29=0\"\r\n" );
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document.write( "Using the zero-factor principle:\r\n" );
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document.write( "We have already seen that \"k=-1\" is not\r\n" );
document.write( "possible, so we only need investigate \"k=0\"\r\n" );
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document.write( "Now we use\"k=0\" and since \"y=0x\", \"y=0\" in the original:\r\n" );
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document.write( "\"system%28x%5E3%2By%5E3=1%2C+x%5E2y%2B2xy%5E2%2By%5E3=2%29\"\r\n" );
document.write( "\"system%28x%5E3%2B%280%29%5E3=1%2C+x%5E2%280%29%2B2x%280%29%5E2%2B%280%29%5E3=2%29\"\r\n" );
document.write( "\"system%28x%5E3=1%2C+0=2%29\"\r\n" );
document.write( "\"system%28x=1%2C+0=2%29\"\r\n" );
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document.write( "This is certainly not true, so Case 3\r\n" );
document.write( "\"k=0\" is not possible since it produces\r\n" );
document.write( "no solutions.\r\n" );
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document.write( "So the only real solutions are:\r\n" );
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document.write( "and\r\n" );
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document.write( "However, there are also some imaginary solutions.  I did not\r\n" );
document.write( "find those. They would require finding the 2 imaginary\r\n" );
document.write( "cube roots each of 4 and 3.  I only considered the real\r\n" );
document.write( "cube roots of 4 and 3.  Post again if you want all the\r\n" );
document.write( "imaginary solutions as well.\r\n" );
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document.write( "Edwin

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