|x| = 5,x = ±5；|y| = 3 ,y = ±3
5 + 3 = 8
5 - 3 = 2
- 5 - 3 = -8 ≠ 8
- 5 + 3 = -2 ≠ 2
所以 有兩組結(jié)果
x = 5,y = 3,則 ³√(x + y) = ³√8 = 2
x = 5,y = -3,則 ³√(x + y) = ³√2
實(shí)際上,當(dāng) x + y > 0 時(shí),|x + y| = x + y,而當(dāng) x + y < 0 時(shí),|x + y| = - (x + y) = -x -y.所以掌握好這個(gè)原則就可以很好的把絕對(duì)值號(hào)去掉了.