The sum of 5 x2 y, 4 x2 y, 8 x2 y is

We are not sure what you mean!. Is it this:5^(x^2) y+4^(x^2) y+8^(x^2) y. If it is, then you can write it this way:(4^(x^2)+5^(x^2)+8^(x^2)) y. That's about it.