document.write( "Question 207639: Solve using completing the square? -3x^2+6x-5 \n" ); document.write( "
Algebra.Com's Answer #157038 by jim_thompson5910(35256)\"\" \"About 
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\n" ); document.write( "\n" ); document.write( "\"-3x%5E2%2B6x-5\" Start with the given expression.\r
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\n" ); document.write( "\n" ); document.write( "\"-3%28x%5E2-2x%2B5%2F3%29\" Factor out the \"x%5E2\" coefficient \"-3\". This step is very important: the \"x%5E2\" coefficient must be equal to 1.\r
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\n" ); document.write( "\n" ); document.write( "Take half of the \"x\" coefficient \"-2\" to get \"-1\". In other words, \"%281%2F2%29%28-2%29=-1\".\r
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\n" ); document.write( "\n" ); document.write( "Now square \"-1\" to get \"1\". In other words, \"%28-1%29%5E2=%28-1%29%28-1%29=1\"\r
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\n" ); document.write( "\n" ); document.write( "\"-3%28x%5E2-2x%2Bhighlight%281-1%29%2B5%2F3%29\" Now add and subtract \"1\" inside the parenthesis. Make sure to place this after the \"x\" term. Notice how \"1-1=0\". So the expression is not changed.\r
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\n" ); document.write( "\n" ); document.write( "\"-3%28%28x%5E2-2x%2B1%29-1%2B5%2F3%29\" Group the first three terms.\r
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\n" ); document.write( "\n" ); document.write( "\"-3%28%28x-1%29%5E2-1%2B5%2F3%29\" Factor \"x%5E2-2x%2B1\" to get \"%28x-1%29%5E2\".\r
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\n" ); document.write( "\n" ); document.write( "\"-3%28%28x-1%29%5E2%2B2%2F3%29\" Combine like terms.\r
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\n" ); document.write( "\n" ); document.write( "\"-3%28x-1%29%5E2-3%282%2F3%29\" Distribute.\r
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\n" ); document.write( "\n" ); document.write( "\"-3%28x-1%29%5E2-2\" Multiply.\r
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\n" ); document.write( "\n" ); document.write( "So after completing the square, \"-3x%5E2%2B6x-5\" transforms to \"-3%28x-1%29%5E2-2\". So \"-3x%5E2%2B6x-5=-3%28x-1%29%5E2-2\".\r
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\n" ); document.write( "\n" ); document.write( "So \"-3x%5E2%2B6x-5=0\" is equivalent to \"-3%28x-1%29%5E2-2=0\".\r
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\n" ); document.write( "\n" ); document.write( "So we can solve \"-3%28x-1%29%5E2-2=0\" in place of solving \"-3x%5E2%2B6x-5=0\"\r
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\n" ); document.write( "\n" ); document.write( "\"-3%28x-1%29%5E2-2=0\" Start with the given equation.\r
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\n" ); document.write( "\n" ); document.write( "\"-3%28x-1%29%5E2=0%2B2\"Add \"2\" to both sides.\r
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\n" ); document.write( "\n" ); document.write( "\"-3%28x-1%29%5E2=2\" Combine like terms.\r
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\n" ); document.write( "\n" ); document.write( "\"%28x-1%29%5E2=%282%29%2F%28-3%29\" Divide both sides by \"-3\".\r
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\n" ); document.write( "\n" ); document.write( "\"%28x-1%29%5E2=-2%2F3\" Reduce.\r
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\n" ); document.write( "\n" ); document.write( "\"x-1=%22%22%2B-sqrt%28-2%2F3%29\" Take the square root of both sides.\r
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\n" ); document.write( "\n" ); document.write( "\"x-1=sqrt%28-2%2F3%29\" or \"x-1=-sqrt%28-2%2F3%29\" Break up the \"plus/minus\" to form two equations.\r
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\n" ); document.write( "\n" ); document.write( "\"x-1=%28i%2Asqrt%286%29%29%2F3\" or \"x-1=-%28i%2Asqrt%286%29%29%2F3\" Simplify the square root. Note: \"i=sqrt%28-1%29\"\r
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\n" ); document.write( "\n" ); document.write( "\"x=1%2B%28i%2Asqrt%286%29%29%2F3\" or \"x=1-%28i%2Asqrt%286%29%29%2F3\" Add \"1\" to both sides.\r
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\n" ); document.write( "\n" ); document.write( "Answer:\r
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\n" ); document.write( "\n" ); document.write( "So the solutions are \"x=1%2B%28i%2Asqrt%286%29%29%2F3\" or \"x=1-%28i%2Asqrt%286%29%29%2F3\".
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