document.write( "Question 173656: Here is one that I am completely stumped on:\r
\n" ); document.write( "\n" ); document.write( "Find a value for k that will make 4x^2 + 6.4x +k a perfect square. Describe the procedure that you used which requires algebra, not trial and error. \r
\n" ); document.write( "\n" ); document.write( "HELP!!! \n" ); document.write( "

Algebra.Com's Answer #128512 by Fombitz(32388) $\"\"$ $\"About$

You can put this solution on YOUR website!
A perfect square would mean,
\n" ); document.write( " $\"4x%5E2+%2B+6.4x+%2Bk=%28ax%2Bb%29%5E2\"$
\n" ); document.write( "If we expand the right hand side, we get,
\n" ); document.write( " $\"%28ax%2Bb%29%5E2=a%5E2%2Ax%5E2%2B%282ab%29x%2Bb%5E2\"$
\n" ); document.write( "Let's compare coefficients with your equation,
\n" ); document.write( "1. $\"a%5E2=4\"$
\n" ); document.write( "2. $\"2ab=6.4\"$
\n" ); document.write( "3. $\"b%5E2=k\"$
\n" ); document.write( "From 1, a can be either 2 or -2.
\n" ); document.write( "Let's start with a=2 and find the others,
\n" ); document.write( "From 2,
\n" ); document.write( " $\"2ab=6.4\"$
\n" ); document.write( " $\"2%282%29b=6.4\"$
\n" ); document.write( " $\"b=6.4%2F4=1.6\"$
\n" ); document.write( "From 3,
\n" ); document.write( " $\"b%5E2=k\"$
\n" ); document.write( " $\"k=%281.6%29%5E2\"$
\n" ); document.write( " $\"k=2.56\"$ \r
\n" ); document.write( "\n" ); document.write( ".
\n" ); document.write( ".
\n" ); document.write( ".
\n" ); document.write( "We can also work with a=-2.
\n" ); document.write( "From 2,
\n" ); document.write( " $\"2ab=6.4\"$
\n" ); document.write( " $\"2%28-2%29b=6.4\"$
\n" ); document.write( " $\"b=6.4%2F%28-4%29=-1.6\"$
\n" ); document.write( "From 3,
\n" ); document.write( " $\"b%5E2=k\"$
\n" ); document.write( " $\"k=%28-1.6%29%5E2\"$
\n" ); document.write( " $\"k=2.56\"$
\n" ); document.write( "And we're led to the same answer. \n" ); document.write( "

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