[tex] (a + b)^n=a^n+\binom{n}{1}a^{n-1}b+\binom{n}{2}a^{n-2}b^2+...
[/tex]
So,
The first term of the binomial expansion [tex](x + y)^4[/tex] is
[tex](x + y)^4 = x^4 + \binom{4}{1}x^{4-1}y+...[/tex]
We only need the first term, so, the first term of the binomial expansion [tex](x + y)^4[/tex] is [tex]x^4[/tex]
