If 1-4x+4x^2=0, then 2x equals

1978 AMC 12 Problem 1

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1-\frac4x+\frac4{x^2}=0,

then

\frac2x

equals

-1

1

2

-1

2

-1

-2

Let

u=\frac2x

The resulting quadratic is a perfect square

With

u=\frac{2}{x},

the equation becomes

1-2u+u^2=0,

(u-1)^2=0.

Therefore

\frac{2}{x}=u=1.

Therefore, the correct answer is B.