Question 177981
Find a value for k that will make 4x^2 + 6.4 x + k a perfect square. 
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4x^2 + 6.4x + k
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Factor out the "4" to get:
4(x^2 = 1.6x + ?
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Add the square of half the coefficient of "x"
4(x^2 + 1.6x + (1.6/2)^2)

k = (1.6/2)^2 = 0.8^2 = 0.64
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Cheers,
Stan H.