document.write( "Question 389186: Please show me how to Solve the equation x2 + 8x – 2 = 0 using both The quadratic formula and Completing the square.
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Algebra.Com's Answer #275723 by jim_thompson5910(35256)\"\" \"About 
You can put this solution on YOUR website!
Solving by use of the quadratic formula:\r
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\n" ); document.write( "\n" ); document.write( "\"x%5E2%2B8x-2=0\" Start with the given equation.\r
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\n" ); document.write( "\n" ); document.write( "Notice that the quadratic \"x%5E2%2B8x-2\" is in the form of \"Ax%5E2%2BBx%2BC\" where \"A=1\", \"B=8\", and \"C=-2\"\r
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\n" ); document.write( "\n" ); document.write( "Let's use the quadratic formula to solve for \"x\":\r
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\n" ); document.write( "\n" ); document.write( "\"x+=+%28-B+%2B-+sqrt%28+B%5E2-4AC+%29%29%2F%282A%29\" Start with the quadratic formula\r
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\n" ); document.write( "\n" ); document.write( "\"x+=+%28-%288%29+%2B-+sqrt%28+%288%29%5E2-4%281%29%28-2%29+%29%29%2F%282%281%29%29\" Plug in \"A=1\", \"B=8\", and \"C=-2\"\r
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\n" ); document.write( "\n" ); document.write( "\"x+=+%28-8+%2B-+sqrt%28+64-4%281%29%28-2%29+%29%29%2F%282%281%29%29\" Square \"8\" to get \"64\". \r
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\n" ); document.write( "\n" ); document.write( "\"x+=+%28-8+%2B-+sqrt%28+64--8+%29%29%2F%282%281%29%29\" Multiply \"4%281%29%28-2%29\" to get \"-8\"\r
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\n" ); document.write( "\n" ); document.write( "\"x+=+%28-8+%2B-+sqrt%28+64%2B8+%29%29%2F%282%281%29%29\" Rewrite \"sqrt%2864--8%29\" as \"sqrt%2864%2B8%29\"\r
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\n" ); document.write( "\n" ); document.write( "\"x+=+%28-8+%2B-+sqrt%28+72+%29%29%2F%282%281%29%29\" Add \"64\" to \"8\" to get \"72\"\r
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\n" ); document.write( "\n" ); document.write( "\"x+=+%28-8+%2B-+sqrt%28+72+%29%29%2F%282%29\" Multiply \"2\" and \"1\" to get \"2\". \r
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\n" ); document.write( "\n" ); document.write( "\"x+=+%28-8+%2B-+6%2Asqrt%282%29%29%2F%282%29\" Simplify the square root (note: If you need help with simplifying square roots, check out this solver) \r
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\n" ); document.write( "\n" ); document.write( "\"x+=+%28-8%29%2F%282%29+%2B-+%286%2Asqrt%282%29%29%2F%282%29\" Break up the fraction. \r
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\n" ); document.write( "\n" ); document.write( "\"x+=+-4+%2B-+3%2Asqrt%282%29\" Reduce. \r
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\n" ); document.write( "\n" ); document.write( "\"x+=+-4%2B3%2Asqrt%282%29\" or \"x+=+-4-3%2Asqrt%282%29\" Break up the expression. \r
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\n" ); document.write( "\n" ); document.write( "So the solutions are \"x+=+-4%2B3%2Asqrt%282%29\" or \"x+=+-4-3%2Asqrt%282%29\" \r
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\n" ); document.write( "\n" ); document.write( "Solving by use of completing the square:\r
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\n" ); document.write( "\n" ); document.write( "First we need to complete the square for the expression \"x%5E2%2B8x-2\"\r
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\n" ); document.write( "\n" ); document.write( "\"x%5E2%2B8x-2\" Start with the given expression.\r
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\n" ); document.write( "\n" ); document.write( "Take half of the \"x\" coefficient \"8\" to get \"4\". In other words, \"%281%2F2%29%288%29=4\".\r
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\n" ); document.write( "\n" ); document.write( "Now square \"4\" to get \"16\". In other words, \"%284%29%5E2=%284%29%284%29=16\"\r
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\n" ); document.write( "\n" ); document.write( "\"x%5E2%2B8x%2Bhighlight%2816-16%29-2\" Now add and subtract \"16\". Make sure to place this after the \"x\" term. Notice how \"16-16=0\". So the expression is not changed.\r
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\n" ); document.write( "\n" ); document.write( "\"%28x%5E2%2B8x%2B16%29-16-2\" Group the first three terms.\r
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\n" ); document.write( "\n" ); document.write( "\"%28x%2B4%29%5E2-16-2\" Factor \"x%5E2%2B8x%2B16\" to get \"%28x%2B4%29%5E2\".\r
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\n" ); document.write( "\n" ); document.write( "\"%28x%2B4%29%5E2-18\" Combine like terms.\r
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\n" ); document.write( "\n" ); document.write( "So after completing the square, \"x%5E2%2B8x-2\" transforms to \"%28x%2B4%29%5E2-18\". So \"x%5E2%2B8x-2=%28x%2B4%29%5E2-18\".\r
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\n" ); document.write( "\n" ); document.write( "So \"x%5E2%2B8x-2=0\" is equivalent to \"%28x%2B4%29%5E2-18=0\".\r
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\n" ); document.write( "\n" ); document.write( "Now let's solve \"%28x%2B4%29%5E2-18=0\"\r
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\n" ); document.write( "\n" ); document.write( "\"%28x%2B4%29%5E2-18=0\" Start with the given equation.\r
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\n" ); document.write( "\n" ); document.write( "\"%28x%2B4%29%5E2=0%2B18\"Add \"18\" to both sides.\r
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\n" ); document.write( "\n" ); document.write( "\"%28x%2B4%29%5E2=18\" Combine like terms.\r
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\n" ); document.write( "\n" ); document.write( "\"x%2B4=%22%22%2B-sqrt%2818%29\" Take the square root of both sides.\r
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\n" ); document.write( "\n" ); document.write( "\"x%2B4=sqrt%2818%29\" or \"x%2B4=-sqrt%2818%29\" Break up the \"plus/minus\" to form two equations.\r
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\n" ); document.write( "\n" ); document.write( "\"x%2B4=3%2Asqrt%282%29\" or \"x%2B4=-3%2Asqrt%282%29\" Simplify the square root.\r
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\n" ); document.write( "\n" ); document.write( "\"x=-4%2B3%2Asqrt%282%29\" or \"x=-4-3%2Asqrt%282%29\" Subtract \"4\" from 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=-4%2B3%2Asqrt%282%29\" or \"x=-4-3%2Asqrt%282%29\".\r
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\n" ); document.write( "\n" ); document.write( "Notice how we get the same answers. So either method works.\r
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\n" ); document.write( "\n" ); document.write( "If you need more help, email me at jim_thompson5910@hotmail.com\r
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\n" ); document.write( "\n" ); document.write( "Also, feel free to check out my tutoring website\r
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\n" ); document.write( "\n" ); document.write( "Jim
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