Question

4c) (4 - 2√5) . (4 + 2√5)

a) - 8
b) - 4
c) 12√5
d) 6 √5

Answer 1

$\left(4-2\sqrt{5}\right)\cdot\left(4+2\sqrt{5}\right)\\\\{4^2-\left(2\sqrt{5}\right)^2}\\\\16-20=\boxed{-4}$