Question

2-root5 × 2 - root 5​

Answer 1

Step-by-step explanation:

$(2 - \sqrt{5} )(2 - \sqrt{5} ) \\ \\ = (2 - \sqrt{5} {)}^{2} \\ \\ (a - b {)}^{2} = {a}^{2} + {b}^{2} - 2ab \\ \\ = (2 {)}^{2} + ( \sqrt{5} {)}^{2} - 2(2 \sqrt{5} ) \\ \\ = 4 + 5 - 4 \sqrt{5} \\ \\ = 9 - 4 \sqrt{5}$