Question

2 $sqrt{20}$-3 $sqrt{45}$+$sqrt{18}$+$sqrt{72}$-$sqrt{80}$

Answer 1

$2sqrt{20}-3sqrt{45}+sqrt{18}+sqrt{72}-sqrt{80}=\=2sqrt{4cdot5}-3sqrt{5cdot9}+sqrt{2cdot9}+sqrt{2cdot36}-sqrt{5cdot16}=\=4sqrt5-9sqrt5+3sqrt2+6sqrt2-4sqrt5=9sqrt2-9sqrt5=9cdotleft(sqrt2-sqrt5right)$