Giúp minh câu 6 với mn ơiii

`6`

`A=(2+sqrt3)^5-(2-sqrt3)^5`

`A=sum_[k=0]^5 C_5^k 2^[5-k] (sqrt3)^k-sum_[k=0]^5 C_5^k 2^[5-k] (-sqrt3)^k`

`A=C_5^0 32+C_5^1 16sqrt3+C_5^2 24+C_5^3 12sqrt3+C_5^4 18+C_5^5 (sqrt3)^5-[C_5^0 32-C_5^1 16sqrt3+C_5^2 24-C_5^3 12sqrt3+C_5^4 18-C_5^5 (sqrt3)^5]`

`A=2C_5^1 16sqrt3+2C_5^3 12sqrt3+2C_5^5 (sqrt3)^5`

`A=160sqrt3+240sqrt3+18sqrt3`

`A=418sqrt3`

`-> {(a=0),(b=418):}`

`a+b=0+418=418`

`-> bbD`