Đa thức P(x) = (1+3x+2x^2)^10 = a0+(a1)x +... + (a20).(x^20).

A. $a_{15}=C_{10}^{10}.C_{10}^5.3^5+C_{10}^9.C_9^6.3^3+C_{10}^8.C_8^7.3$.

B. $a_{15}=C_{10}^{10}.C_{10}^5.2^5+C_{10}^9.C_9^6.2^6+C_{10}^8.C_8^7.2^7$.

C. $a_{15}=C_{10}^{10}.C_{10}^5.2^5+C_{10}^9.C_9^6.3^3.2^6+C_{10}^8.C_8^7.2^7$.

D.$a_{15}=C_{10}^{10}.C_{10}^5.3^5.2^5+C_{10}^9.C_9^6.2^6+C_{10}^8.C_8^7.3.2^7$.