Answer:
Applying the binomial theorem
[tex]{\displaystyle (x+a)^{n}=\sum _{k=0}^{n}{n \choose k}x^{n-k}a^{k}}[/tex]
Here we have x = -[tex]\sqrt{2}[/tex], n = 8,
=> 4th term (k = 3) would be:
[tex]{8 \choose 3}x^{8-3}a^{3}} = {8 \choose 3}(-\sqrt{2})^{5}a^{3}} = -224a^{3}\sqrt{2}[/tex]
Hope this helps!
:)
