(sqrt30+sqrt21-3)(sqrt3+sqrt10-sqrt7)
=根号3*(根号10 + 根号7 - 根号3)[根号10-(根号7 - 根号3)]
=根号3*[(根号10)²-(根号7 - 根号3)²]
=根号3*[10-(7-2根号21 +3）]
=根号3 * 2根号21
=6根号7