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Q.
Number of terms in the expansion of
$(1+5 \sqrt{2} x)^{9}+(1-5 \sqrt{2} x)^{9}$ is
Binomial Theorem
Solution:
If $n$ is odd, then the expansion of $(x+a)^{n}+(x-a)^{n}$
contains $\left(\frac{ n +1}{2}\right)$ terms. So, the expansion
of $(1+5 \sqrt{2} x )^{9}+(1-5 \sqrt{2} x )^{9} \operatorname{has}\left(\frac{9+1}{2}\right)=5$ terms