Question

корень16c+2корень40c-3корень90c

Answer 1

$sqrt{16c} +2 sqrt{40c} -3 sqrt{90c} = 4sqrt{c} +4 sqrt{10c} -9 sqrt{10c} = \ =4sqrt{c} -5 sqrt{10c}$
$= sqrt{c} (4-5 sqrt{10} )$