(x-1/x)^9=x^9-(C1 9)x^7+(C2 9)x^5-(C3 9)x³+(C4 9)x-(C5 9)(1/x)+(C6 9)(1/x³)-(C7 9)(1/x^5)+(C8 9)(1/x^7)-(1/x^9)所以含有x³ 的项为-(C3 9)x³=-84x³
