Question

Cat face (2- radical din 5)^2 ??

Answer 1

$(2 - \sqrt{5}) ^{2} = {2}^{2} - 2 \times 2 \sqrt{5} + { \sqrt{5} }^{2} = 4 - 2 \times 2 \sqrt{5} + { \sqrt{5} }^{2} = 4 - 2 \times 2 \sqrt{5} + 5 = 4 - 4 \sqrt{5} + 5 = 9 - 4 \sqrt{5}$

Answer 2

$\it (a-b)^2 =a^2-2ab+b^2\\ \\ (2-\sqrt5)^2 = 2^2-2\cdot2\cdot\sqrt5 +(\sqrt5)^2 =4-4\sqrt5+5=9-4\sqrt5$