document.write( "Question 199774: Hello!\r
\n" ); document.write( "\n" ); document.write( "Find all real zeros of the polynomial. Use the quadratic formula if necessary\r
\n" ); document.write( "\n" ); document.write( "P(x) = x^4 + x^3 - 5x^2 - 4x + 4 \r
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Algebra.Com's Answer #150142 by jim_thompson5910(35256)\"\" \"About 
You can put this solution on YOUR website!
First, let's find the possible rational zeros of P(x):\r
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\n" ); document.write( "\n" ); document.write( "Any rational zero can be found through this equation\r
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\n" ); document.write( "\n" ); document.write( " where p and q are the factors of the last and first coefficients\r
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\n" ); document.write( "\n" ); document.write( "So let's list the factors of 4 (the last coefficient):\r
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\n" ); document.write( "\n" ); document.write( "Now let's list the factors of 1 (the first coefficient):\r
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\n" ); document.write( "\n" ); document.write( "Now let's divide each factor of the last coefficient by each factor of the first coefficient\r
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\n" ); document.write( "\n" ); document.write( "Now simplify\r
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\n" ); document.write( "\n" ); document.write( "These are all the distinct rational zeros of the function that could occur\r
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\n" ); document.write( "\n" ); document.write( "Now let's see which possible roots are actually roots.\r
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\n" ); document.write( "\n" ); document.write( "Let's see if the possible zero \"1\" is really a root for the function \"x%5E4%2Bx%5E3-5x%5E2-4x%2B4\"\r
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\n" ); document.write( "\n" ); document.write( "So let's make the synthetic division table for the function \"x%5E4%2Bx%5E3-5x%5E2-4x%2B4\" given the possible zero \"1\":\r
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1|11-5-44
| 12-3-7
12-3-7-3
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\n" ); document.write( "\n" ); document.write( "Since the remainder \"-3\" (the right most entry in the last row) is not equal to zero, this means that \"1\" is not a zero of \"x%5E4%2Bx%5E3-5x%5E2-4x%2B4\"\r
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\n" ); document.write( "\n" ); document.write( "Let's see if the possible zero \"2\" is really a root for the function \"x%5E4%2Bx%5E3-5x%5E2-4x%2B4\"\r
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\n" ); document.write( "\n" ); document.write( "So let's make the synthetic division table for the function \"x%5E4%2Bx%5E3-5x%5E2-4x%2B4\" given the possible zero \"2\":\r
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2|11-5-44
| 262-4
131-20
\r
\n" ); document.write( "\n" ); document.write( "Since the remainder \"0\" (the right most entry in the last row) is equal to zero, this means that \"2\" is a zero of \"x%5E4%2Bx%5E3-5x%5E2-4x%2B4\"\r
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\n" ); document.write( "\n" ); document.write( "So this means that \"x%5E4%2Bx%5E3-5x%5E2-4x%2B4=%28x-2%29%28x%5E3%2B3x%5E2%2Bx-2%29\"\r
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\n" ); document.write( "\n" ); document.write( "Note: the term \"x%5E3%2B3x%5E2%2Bx-2\" was formed by the first four values in the bottom row.\r
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\n" ); document.write( "\n" ); document.write( "Now that you have \"x%5E3%2B3x%5E2%2Bx-2\", you simply find the possible rational zeros for \"x%5E3%2B3x%5E2%2Bx-2\" and test to see which ones are really zeros (ie repeat the first two steps).\r
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\n" ); document.write( "\n" ); document.write( "It turns out that the possible roots for \"x%5E3%2B3x%5E2%2Bx-2\" are: 1, 2, -1, -2\r
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\n" ); document.write( "\n" ); document.write( "and that -2 is a root of \"x%5E3%2B3x%5E2%2Bx-2\"\r
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\n" ); document.write( "\n" ); document.write( "Here's the synthetic division to prove it:\r
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-2|131-2
| -2-22
11-10
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\n" ); document.write( "\n" ); document.write( "Looking at the bottom row of values (everything but the remainder), we get \"x%5E2%2Bx-1\". So this means that\r
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\n" ); document.write( "\n" ); document.write( "\"x%5E3%2B3x%5E2%2Bx-2=%28x%2B2%29%28x%5E2%2Bx-1%29\"\r
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\n" ); document.write( "\n" ); document.write( "Note: this consequently means that \"x%5E4%2Bx%5E3-5x%5E2-4x%2B4=%28x-2%29%28x%2B2%29%28x%5E2%2Bx-1%29\"\r
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\n" ); document.write( "\n" ); document.write( "Now we just need to solve \"x%5E2%2Bx-1=0\" to find the last remaining zeros.\r
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\n" ); document.write( "\n" ); document.write( "\"x%5E2%2Bx-1=0\" Start with the given equation.\r
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\n" ); document.write( "\n" ); document.write( "Notice we have a quadratic in the form of \"Ax%5E2%2BBx%2BC\" where \"A=1\", \"B=1\", and \"C=-1\"\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-%281%29+%2B-+sqrt%28+%281%29%5E2-4%281%29%28-1%29+%29%29%2F%282%281%29%29\" Plug in \"A=1\", \"B=1\", and \"C=-1\"\r
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\n" ); document.write( "\n" ); document.write( "\"x+=+%28-1+%2B-+sqrt%28+1-4%281%29%28-1%29+%29%29%2F%282%281%29%29\" Square \"1\" to get \"1\". \r
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\n" ); document.write( "\n" ); document.write( "\"x+=+%28-1+%2B-+sqrt%28+1--4+%29%29%2F%282%281%29%29\" Multiply \"4%281%29%28-1%29\" to get \"-4\"\r
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\n" ); document.write( "\n" ); document.write( "\"x+=+%28-1+%2B-+sqrt%28+1%2B4+%29%29%2F%282%281%29%29\" Rewrite \"sqrt%281--4%29\" as \"sqrt%281%2B4%29\"\r
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\n" ); document.write( "\n" ); document.write( "\"x+=+%28-1+%2B-+sqrt%28+5+%29%29%2F%282%281%29%29\" Add \"1\" to \"4\" to get \"5\"\r
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\n" ); document.write( "\n" ); document.write( "\"x+=+%28-1+%2B-+sqrt%28+5+%29%29%2F%282%29\" Multiply \"2\" and \"1\" to get \"2\". \r
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\n" ); document.write( "\n" ); document.write( "\"x+=+%28-1%2Bsqrt%285%29%29%2F%282%29\" or \"x+=+%28-1-sqrt%285%29%29%2F%282%29\" Break up the expression. \r
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\n" ); document.write( "\n" ); document.write( "So the last two roots are \"x+=+%28-1%2Bsqrt%285%29%29%2F%282%29\" or \"x+=+%28-1-sqrt%285%29%29%2F%282%29\" \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 four zeros of \"P%28x%29+=+x%5E4+%2B+x%5E3+-+5x%5E2+-+4x+%2B+4+\"are:\r
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\n" ); document.write( "\n" ); document.write( "\"x=2\", \"x=-2\", \"x+=+%28-1%2Bsqrt%285%29%29%2F%282%29\" or \"x+=+%28-1-sqrt%285%29%29%2F%282%29\"\r
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\n" ); document.write( "\n" ); document.write( "Note: if you wanted to, you could compactly write the zeros as:\r
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\n" ); document.write( "\n" ); document.write( "\"x=%22%22%2B-+2\", \"x+=+%28-1%2B-sqrt%285%29%29%2F%282%29\"\r
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\n" ); document.write( "\n" ); document.write( "just remember that there are 4 zeros.\r
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\n" ); document.write( "\n" ); document.write( "If you have any questions, email me at jim_thompson5910@hotmail.com.
\n" ); document.write( "Check out my website if you are interested in tutoring.
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