If [tex] x = \left(\frac{5-\sqrt{2}}{2}\right) [/tex], find [tex] \left(x^3 + \frac{1}{x^3}\right) - 5\left(x^3 + \frac{1}{x^2}\right) + \left(x + \frac{1}{x}\right) [/tex].



Answer :

Given [tex]\( x = \left(\frac{5 - \sqrt{2}}{2}\right) \)[/tex], let's break down the problem step by step to find the value of the expression:

[tex]\[ \left(x^3 + \frac{1}{x^3}\right) - 5\left(x^3 + \frac{1}{x^2}\right) + \left(x + \frac{1}{x}\right) \][/tex]

1. Calculate [tex]\( x^3 \)[/tex]:
[tex]\[ x^3 \approx 5.7632 \][/tex]

2. Calculate [tex]\( \frac{1}{x^3} \)[/tex]:
[tex]\[ \frac{1}{x^3} \approx 0.1735 \][/tex]

3. Calculate [tex]\( x^3 + \frac{1}{x^3} \)[/tex]:
[tex]\[ x^3 + \frac{1}{x^3} \approx 5.7632 + 0.1735 = 5.9367 \][/tex]

4. Calculate [tex]\( \frac{1}{x^2} \)[/tex]:
[tex]\[ \frac{1}{x^2} \approx 0.3111 \][/tex]

5. Calculate [tex]\( x^3 + \frac{1}{x^2} \)[/tex]:
[tex]\[ x^3 + \frac{1}{x^2} \approx 5.7632 + 0.3111 = 6.0743 \][/tex]

6. Multiply this result by 5:
[tex]\[ 5 \left( x^3 + \frac{1}{x^2} \right) \approx 5 \times 6.0743 = 30.3714 \][/tex]

7. Calculate [tex]\( \frac{1}{x} \)[/tex]:
[tex]\[ \frac{1}{x} \approx 0.5578 \][/tex]

8. Calculate [tex]\( x + \frac{1}{x} \)[/tex]:
[tex]\[ x + \frac{1}{x} \approx 1.7929 + 0.5578 = 2.3507 \][/tex]

Finally, combine all the parts of the expression:
[tex]\[ (x^3 + \frac{1}{x^3}) - 5(x^3 + \frac{1}{x^2}) + (x + \frac{1}{x}) \approx 5.9367 - 30.3714 + 2.3507 = -22.0841 \][/tex]

Thus, the value of the expression is approximately
[tex]\[ -22.0841 \][/tex]