Question

(5+underoot 5) (5- underoot 5)​

Answer 1

$\huge\sf\fbox\blue{✬ Äñswêr ✬}$

$(5 + \sqrt{5} )(5 - \sqrt{5} )$

$5(5 - \sqrt{5} ) + \sqrt{5} (5 - \sqrt{5} )$

$25 - 5 \sqrt{5} + 5 \sqrt{5} - 5$

$= 25 - 5$

$= 20$

$\huge\sf\fbox\purple{or}$

Using identity

$(a + b)(a - b) = {a}^{2} - {b}^{2}$

$(5 + \sqrt{5} )(5 - \sqrt{5} ) = {5}^{2} - ({ \sqrt{5} })^{2}$

$25 - ( \sqrt{5} \times \sqrt{5} )$

$= 25 - 5$

$= 20$