`~rai~`
\(\text{Áp dụng nhị thức Newton ta có:}\\\left(x^3+\dfrac{1}{x}\right)^7\\=C_7^0(x^3)^7+C_7^1(x^3)^6.\dfrac{1}{x}+C_7^2(x^3)^5\left(\dfrac{1}{x}\right)^2+C_7^3(x^3)^4\left(\dfrac{1}{x}\right)^3+C_7^4(x^3)^3\left(\dfrac{1}{x}\right)^4+C^5_7(x^3)^2\left(\dfrac{1}{x}\right)^5+C_7^6x^3\left(\dfrac{1}{x}\right)^6+C_7^7\left(\dfrac{1}{x}\right)^7\\=x^{21}+7x^{17}+21x^{13}+35x^9+35x^5+21x+\dfrac{7}{x^3}+\dfrac{1}{x^7}.\)
