Answer
$x^{9}-27x^{8}+324x^{7}$
Work Step by Step
Need to find the first three terms.
Apply Binomial Theorem.
$(a+b)^n=\sum_{r=0}^n\dbinom{n}{r}(a)^{n-r}b^r$
$(x-3)^9=\dbinom{9}{0}(x)^9(-3)^0+\dbinom{9}{1}(x)^8(-3)^1+\dbinom{9}{2}(x)^7(-3)^2$
or, $=x^{9}+(9)(x^{8}(-3)+324x^{7}$
or, $=x^{9}-27x^{8}+324x^{7}$
