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Hi,

How did you arrive at
\(5(1+\sqrt{2}) + 2 = 7 + \sqrt{2}\)

Isn't, \(5(1 + \sqrt{2}) + 2 = 5 + 5\sqrt{2} + 2 = 7 + 5\sqrt{2}\)

gmatophobia


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

\(x^2 - 2x + 1 = 0\)

The roots of the equation can be found out by the formula \(\frac{-b \pm\sqrt{b^2 - 4ac}}{2a}\)

Roots = \(\frac{2 \pm\sqrt{4+4}}{2}\)

Roots = \(\frac{2 \pm\sqrt{8}}{2}\)

= \(\frac{2 \pm2\sqrt{2}}{2}\) = \(1\pm\sqrt{2}\)

Let's take only one root to calculate the value of \(x^2\) and \(x^3\)

\(x = 1 + \sqrt{2}\)

\(x^3 = x^2 * x = (1+\sqrt{2})^2 * (1+\sqrt{2}) = 7 + \sqrt{2}\)

Using the option we can see that the value of \(x^3\) matches that of option B

Option B ⇒ 5x + 2

\(5(1+\sqrt{2}) + 2 = 7 + \sqrt{2}\)

Option B
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radhikamehta
Hi,

How did you arrive at
\(5(1+\sqrt{2}) + 2 = 7 + \sqrt{2}\)

Isn't, \(5(1 + \sqrt{2}) + 2 = 5 + 5\sqrt{2} + 2 = 7 + 5\sqrt{2}\)


That must be a typo, another way to approach this problem is:

\(x^3 = x^2 * x\)

Subs. value of \(x^2\)

\(x^3 = (2x + 1)x\)

= \(2x^2 + x\)

Subs. value of \(x^2\)

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

= \(4x + 2 + x\)

= \(5x + 2\)
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