Answer
$x^{16}+24x^{14}+252x^{12}$
Work Step by Step
Need to find the first three terms.
Apply Binomial Theorem.
$(a+b)^n=\sum_{r=0}^n\dbinom{n}{r}(a)^{n-r}b^r$
$(x^2+3)^8=\dbinom{8}{0}(x^2)^8(3)^0+\dbinom{8}{1}(x^2)^7(3)^1+\dbinom{8}{2}(x^2)^6(3)^2$
or, $=x^{16}+(8)(x^{14}(3)+252x^{12}$
or, $=x^{16}+24x^{14}+252x^{12}$
