document.write( "Question 883719: how do you factor x^4 - X^2 - 20. I got (x^2+4)(x^2-5) but it is supposedly the wrong answer. Also tried x^2(x+1)(x-1)-20. still wrong. \n" ); document.write( "

Algebra.Com's Answer #533705 by josgarithmetic(39617) $\"\"$ $\"About$

You can put this solution on YOUR website!
X is a misprint. \r
\n" ); document.write( "\n" ); document.write( "Starting from $\"x%5E4-x%5E2-20\"$ try conveniently substituting like $\"u=x%5E2\"$ and rewrite the expression as $\"u%5E2-u-20\"$ . You can take your guesses using 5 and 4 and hopefully find $\"%28u%2B4%29%28u-5%29\"$ , and this obviously works ----- the expression using u.\r
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\n" ); document.write( "\n" ); document.write( "Now substitute back for u:
\n" ); document.write( " $\"highlight%28%28x%5E2%2B4%29%28x%5E2-5%29%29\"$ .
\n" ); document.write( "The answer key is wrong.
\n" ); document.write( "YOUR first result was correct. \n" ); document.write( "

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