How do you solve by completing the square: $4x^2 + 8x + 20 = 0$ ?

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How do you solve by completing the square: $4x^2 + 8x + 20 = 0$ ?

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Answer 1 · 2015-04-02T13:05:52

Try this:
$4x^2+8x=-20$
$x^2+8/4x=-20/4$
$x^2+2x=-5$
$x^2+2x+1-1=-5$
$(x+1)^2=-5+1$
$(x+1)^2=-4$
$x+1=+-sqrt(-4)$ NEGATIVE ROOT!
If you already saw complex numbers you have:
$x+1=+-[sqrt(4)sqrt(-1)]$
$x=-1+-2i$

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How do you solve by completing the square: $4x^2 + 8x + 20 = 0$ ?

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