Câu 30:
Nếu Cn1+6Cn2+6Cn3=9n2−14nC_{n}^{1}+6C_{n}^{2}+6C_{n}^{3}=9{{n}^{2}}-14nCn1+6Cn2+6Cn3=9n2−14n thì n bằng:
