Question

please show this question.

Answer 1

${a}^{2} + \frac{1}{ {a}^{2} } = 7 \\ a + \frac{1}{a} = \sqrt{9} = 3 \: as \: \: a > 0 \\ now \: \: \: {a}^{3} + \frac{1}{ {a}^{3} } = ( {a}^{2} + \frac{1}{ {a}^{2} } )(a + \frac{1}{a } ) - (a + \frac{1}{a} ) = 7 \times 3 - 3 = 21 - 3 = 18$
ans 18