document.write( "Question 722966: My daughter has a question on a chapter review that I cannot figure out. She is to factor and check 16x^2 + 81. If it were 16x^2-81, I could understand it as (4x+9)(4x-9) and that checks out, but I cannot seem to figure out the equation as it is written. Can you help me please? \n" ); document.write( "
Algebra.Com's Answer #442960 by Edwin McCravy(20054)\"\" \"About 
You can put this solution on YOUR website!
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document.write( "If she has studied imaginary numbers she can factor it,\r\n" );
document.write( "since i² = -1  and therefore\r\n" );
document.write( "     -i² = 1\r\n" );
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document.write( "16x² + 81 =\r\n" );
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document.write( "16x² + 81·1\r\n" );
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document.write( "Now substitute -i² for the 1\r\n" );
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document.write( "16x² + 81·(-i²)\r\n" );
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document.write( "16x² - 81i²\r\n" );
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document.write( "(4x - 9i)(4x + 9i)\r\n" );
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document.write( "However if she has not studied imaginary numbers, then she\r\n" );
document.write( "should just write \"prime\". \r\n" );
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document.write( "Edwin
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