document.write( "Question 892918: Completing the square
\n" ); document.write( "1. X^4+64y^4
\n" ); document.write( "2. X^4+y^2+25
\n" ); document.write( "3. X^4-11x^2y^2+y^4
\n" ); document.write( "
\n" ); document.write( "Please do help me,\r
\n" ); document.write( "\n" ); document.write( "My teacher's solution goes like this, and I didn't even understand cuz he's too fast.\r
\n" ); document.write( "\n" ); document.write( "Ex. x^4+2x^2y^2+9y^4
\n" ); document.write( "x^4+9y^4+2x^2y^2
\n" ); document.write( "x^4+2x^2(3y^2)+9y^4+2x^2y^2-@x^2(3y^2)
\n" ); document.write( "X^4+6x^2y^2+9y^4+2x^2y^2-6x^2y^2
\n" ); document.write( "(x^2+3y^2)^2-4x^2y^2
\n" ); document.write( "(x^2+3y^2)^2-(2xy)^2
\n" ); document.write( "(x^2+3y^2+2xy)(x^2+3y^2-2xy)\r
\n" ); document.write( "\n" ); document.write( "
\n" ); document.write( "

Algebra.Com's Answer #541040 by KMST(5328)\"\" \"About 
You can put this solution on YOUR website!
Look for terms that are squares. It is not easy to see them at first. It takes practice.
\n" ); document.write( "
\n" ); document.write( "I will over-explain your teacher's solution:
\n" ); document.write( "In \"x%5E4%2B2x%5E2y%5E2%2B9y%5E4\" your teacher sees two squares: \"%28x%5E2%29%5E2=red%28x%5E4%29\" and \"%283y2%29%5E2=red%289y%5E4%29\" .
\n" ); document.write( "The expressions \"x%5E2\" and \"3y%5E2\" , squared, appear in \"red%28x%5E4%29%2B2x%5E2y%5E2%2Bred%289y%5E4%29\" .
\n" ); document.write( "If we add those two expressions and square the sum we have
\n" ); document.write( "
\n" ); document.write( "To make the square \"red%28x%5E4%29%2Bgreen%282x%5E2%283y%5E2%29%29%2Bred%289y%5E4%29\" appear,
\n" ); document.write( "your teacher does some plastic surgery to \"red%28x%5E4%29%2B2x%5E2y%5E2%2Bred%289y%5E4%29\" .
\n" ); document.write( "He takes something out of one end and adds it to another place, just like a plastic surgeon would.
\n" ); document.write( "He adds \"green%282x%5E2%283y%5E2%29%29\" to \"complete the square\",
\n" ); document.write( "and subtracts the same \"green%282x%5E2%283y%5E2%29%29\" so as not to really change anything.
\n" ); document.write( "Doing that to \"red%28x%5E4%29%2B2x%5E2y%5E2%2Bred%289y%5E4%29\" , he gets
\n" ); document.write( "
\n" ); document.write( "Of course, he knows that \"green%282x%5E2%283y%5E2%29%29=green%286x%5E2y%5E2%29\"
\n" ); document.write( "and thinks that \"green%286x%5E2y%5E2%29\" is a more elegant way to write it so he writes
\n" ); document.write( "
\n" ); document.write( "The first three terms are his completed square,
\n" ); document.write( "
\n" ); document.write( "and now he writes that as \"%28x%5E2%2B3y%5E2%29%5E2\" for short,
\n" ); document.write( "and he should have written
\n" ); document.write( "\"%28x%5E2%2B3y%5E2%29%5E2%2B2x%5E2y%5E2-green%286x%5E2y%5E2%29\"
\n" ); document.write( "Collecting like terms, he gets
\n" ); document.write( "\"%28x%5E2%2B3y%5E2%29%5E2-4x%5E2y%5E2\"
\n" ); document.write( "Now he realizes that \"4x%5E2y%5E2=%282xy%29%5E2\" is also a square, and re-writes his expression as
\n" ); document.write( "\"%28x%5E2%2B3y%5E2%29%5E2-%282xy%29%5E2\"
\n" ); document.write( "He likes that because now he has a difference of squares,
\n" ); document.write( "and he knows that \"A%5E2-B%5E2=%28A%2BB%29%28A-B%29\" for any two expressions \"A\" and \"B\" .
\n" ); document.write( "So, with \"A=x%5E2%2B3y%5E2\" and \"B=2xy\"
\n" ); document.write( "
\n" ); document.write( "Of course, we do not need those parentheses around \"x%5E2%2B3y%5E2\" and around \"2xy\" ,
\n" ); document.write( "I just wrote those parentheses so you would see the separate expressions.
\n" ); document.write( "So your teacher writes, without unnecessary parentheses,
\n" ); document.write( "\"%28x%5E2%2B3y%5E2%2B2xy%29%28x%5E2%2B3y%5E2-2xy%29\"
\n" ); document.write( "
\n" ); document.write( "1. \"x%5E4%2B64y%5E4=%28x%5E2%29%5E2%2B%288y%5E2%29%5E2\" (I found two squares that are added).
\n" ); document.write( "That could be part of the square of a sum:
\n" ); document.write( "
\n" ); document.write( "To make the complete square \"%28x%5E2%2B16y%5E2%29%5E2=x%5E4%2Bgreen%2816x%5E2y%5E2%29%2B64y%5E4\"
\n" ); document.write( "appear in \"x%5E4%2B64y%5E4\" , I add and subtract \"green%2816x%5E2y%5E2%29\"
\n" ); document.write( "to get \"x%5E4%2Bgreen%2832x%5E2y%5E2%29%2B64y%5E4-green%2832x%5E2y%5E2%29\" .
\n" ); document.write( "I can re-write that as \"%28x%5E2%2B8y%5E2%29%5E2-green%2816x%5E2y%5E2%29\" .
\n" ); document.write( "Then, since \"%284xy%29%5E2\" is a also a square, I have the difference of squares
\n" ); document.write( "\"%28x%5E2%2B8y%5E2%29%5E2-%284xy%29%5E2%29\" , and I can re-write it as
\n" ); document.write( "\"%28x%5E2%2B8y%5E2%2B4xy%29%28x%5E2%2B8y%5E2-4xy%29\"
\n" ); document.write( "
\n" ); document.write( "For 2. \"x%5E4%2By%5E2%2B25\" and 3. \"x%5E4%2By-11x%5E2y%5E2%2By%5E4\" , I see some squares, but I do not immediately see what to do with them.\r
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "2. \"x%5E4%2By%5E2%2B25\" has three squares: \"x%5E4=%28x%5E2%29%5E2\" , \"y%5E2=%28y%29%5E2\" , and \"25=5%5E2\"
\n" ); document.write( "
\n" ); document.write( "3. \"x%5E4%2By-11x%5E2y%5E2%2By%5E4\" has the squares \"x%5E4=%28x%5E2%29%5E2\" and\"y%5E4=%28y%5E2%29%5E2\" .
\n" ); document.write( "
\n" );