`(2x+1)^4+(3+x)^5`
`=(2x)^4+4.(2x)^3+6.(2x)^2+4.(2x)+1+x^5+5.x^4.3+10.x^3.9+10.x^2.27+5.x.81+243`
`=16x^4+32x^3+24x^2+8x+1+x^5+15x^4+90x^3+270x^2+405x+243`
`=x^5+31x^4+122x^3+294x^2+413x+244`
`text{công thức}`
`(a+b)^4=a^4+4a^3b+6a^2b^2+4ab^3+b^4`
`(a+b)^5=a^5+5a^4b+10a^3b^2+10a^2b^3+5ab^4+b^5`