Posted by **Dippy** on Wednesday, March 4, 2009 at 2:26am.

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. I have the answer and it is k = 1.6^2 or 2.56 i just don't get how we got there

- algebra 1 -
**drwls**, Wednesday, March 4, 2009 at 2:37am
I gave you the answer yesterday. I picked 2.56 because

4x^2 + 6.4x + 2.56 = (2x + 1.6)^2

is a "perfect square", as you can verify by multiplication.

1.6 is the number which, when multiplied by twice the square root of 4 (the first coefficient) gives the second coefficient, 6.4.

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