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If \(x^2 - 4x + 1 = 0\), what is \(x^2 + \frac{1}{x^2}\)?

To answer a question like this one, we can begin by comparing what we have with what we need.

We have \(x^2 - 4x + 1 = 0\).

We need \(x^2 + \frac{1}{x^2}\).

Considering them carefully, we may pick up on the \(x^2 + 1\) pattern in both of them.

Then, to make \(x^2 - 4x + 1\) more like \(x^2 + \frac{1}{x^2}\) we can subtract \(4x\) from both sides of the equation to get the following:

\(x^2 + 1 = 4x\)

Then, to make \(x^2 + 1 = 4x\) more like \(x^2 + \frac{1}{x^2}\), we can divide both side by x.

\(x + \frac{1}{x} = 4\)

Now, square both sides.

\(x^2 + 2 + \frac{1}{x^2} = 16\)

\(x^2 + \frac{1}{x^2} = 14\)

A. \(14\)

B. \(16\)

C. \(18\)

D. \(20\)

E. \(22\)­


Correct answer: A
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I wouldn’t do this in a math class, but there’s a shortcut if you realize that 4^ 2 =16 = 4 times 4
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We look at the quadratic equation and see that the product of the roots to be 1 to result in this we must have this property that the roots are reciprocal to each other therefore, x, 1/x are the roots of the equation,
now we know that the sum of the roots =4
x+1/x = 4 square on both sides and simplify we get x^2 + 1/x^2 = 14
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That's a great way to approach, thanks
sriramsundaram91
We look at the quadratic equation and see that the product of the roots to be 1 to result in this we must have this property that the roots are reciprocal to each other therefore, x, 1/x are the roots of the equation,
now we know that the sum of the roots =4
x+1/x = 4 square on both sides and simplify we get x^2 + 1/x^2 = 14
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