Respuesta :

The binomial formula is the following:
[tex](x+y)^4=\Sigma_{k=0}^4C_4^kx^ky^{4-k}\\=y^4+xy^3C_4^1+x^2y^2C_4^2\\+x^3yC_4^2+x^4\\=y^4+4xy^3+6x^2y^2+4x^3y+x^4[/tex]
We have used the formula:
[tex]C_4^k=\dfrac{4!}{(4-k)!k!}[/tex]
k goes from 0 to 4.