Sagot :
2√45 + √81 - 3√20 + 2 = 2√(9 × 5) + √(9 × 9) - 3√(4 × 5) + 2
= 2√9 × √5 + √9² - 3√4 × √5 + 2
= 2 × 3 × √5 + 9 - 3 × 2 × √5 + 2
= 6√5 + 9 - 6√5 + 2
= 11