document.write( "Question 705265: 5x^2-5x=150 found solution using quadratic equation to be 6 and -5.\r
\n" ); document.write( "\n" ); document.write( "6^2=36 5*36=180
\n" ); document.write( " 5*6=30
\n" ); document.write( " 180-30=150\r
\n" ); document.write( "\n" ); document.write( "Use solution in original equation, 6 works, but for the life of me I cannot figure out what I am doing wrong with the -5 solution.
\n" ); document.write( "-5^2=-25 -25*5=-125\r
\n" ); document.write( "\n" ); document.write( "Thanks\r
\n" ); document.write( "\n" ); document.write( "5*-5=-25\r
\n" ); document.write( "\n" ); document.write( "-125 --25=100 \n" ); document.write( "
Algebra.Com's Answer #434793 by jsmallt9(3758)\"\" \"About 
You can put this solution on YOUR website!
6 and -5 are the correct solutions.

\n" ); document.write( "When you check -5 as a solution you are supposed to replace the x's in:
\n" ); document.write( "\"5x%5E2-5x=150\"
\n" ); document.write( "with a -5. In the first term, the x is being squared. So when we replace it with -5, the -5 should be squared, too. A proper replacement of the x's with 6's and -5's would look like:
\n" ); document.write( "\"5%286%29%5E2-5%286%29=150\"
\n" ); document.write( "and
\n" ); document.write( "\"5%28-5%29%5E2-5%28-5%29=150\"
\n" ); document.write( "Notice the parentheses!! They make little difference with the replacements with 6's. But they are critical when replacing the x's with -5! So it is an extremely good habit to use parentheses when making substitutions.

\n" ); document.write( "Your mistake was not using the parentheses and then finding
\n" ); document.write( "-5^2
\n" ); document.write( "which means \"the negative of 5 squared\" which is, of course, -25.
\n" ); document.write( "What you should have been doing was
\n" ); document.write( "(-5)^2
\n" ); document.write( "which means \"the square of -5\" which is, of course, 25. With a 25 instead of -25 you will find that -5 does check out. \n" ); document.write( "
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