## Encyclopedia > Electric light

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# Electric light

Types of electric lighting device include:

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 Quadratic formula ... y = b/(2a), so we add the square of b/(2a) to both sides, getting $x^2+\frac{b}{a}x+\frac{b^2}{4a^2}=-\frac{c}{a}+\frac{b^2}{4a^2}.$ The left ...