is there a formula of (x + y)^(1/3)?

seem like I can't find any formula of (x + y)^(1/a) where as a is positive integer and a >= 2

I only see this formula like this

for example

(x+y)^2 = (x^2)+2xy+(y^2)

(x+y)^3 = (x^3)+3(x^2)y+3x(y^2)+(y^3)

(x+y)^4 = (x^4)+4(x^3)y+(6x^2)(y^2)+4x(y^3)+(y^4)

(x+y)^5 = (x^5)+5(x^4)y+10(x^3)(y^2)+10(x^2)(y^3)+5x(y^4)+(y^5)

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and so on