`~rai~`
\(\text{Áp dụng nhị thức Newton ta có:}\\\left(x^2-\dfrac{2}{x^2}\right)^7\\=C_7^0(x^2)^7+C_7^1(x^2)^6\left(-\dfrac{2}{x^2}\right)+C_7^2(x^2)^5\left(-\dfrac{2}{x^2}\right)^2+C_7^3(x^2)^4\left(-\dfrac{2x}{x^2}\right)^3+C_7^4(x^2)^3\left(-\dfrac{2}{x^2}\right)^4+C_7^5(x^2)^2\left(-\dfrac{2}{x^2}\right)^5+C_7^6x^2\left(-\dfrac{2}{x^2}\right)^6+C_7^7\left(-\dfrac{2}{x^2}\right)^7\\=x^{14}-14x^{10}+84x^6-280x^2+\dfrac{560}{x^2}-\dfrac{672}{x^6}+\dfrac{448}{x^{10}}-\dfrac{128}{x^{14}}.\)
