If $P(n): 2^{n} < n!$,then the smallest positive integer $n$ for which $P(n)$ is true is:

Prove the following by using the principle of mathematical induction for all $n \in N$:
$1^{2}+3^{2}+5^{2}+\ldots+(2n-1)^{2}=\frac{n(2n-1)(2n+1)}{3}$

Prove the following by using the principle of mathematical induction for all $n \in N:$
$3 \times 6 + 6 \times 9 + 9 \times 12 + \ldots + (3n)(3n + 3) = 3n(n + 1)(n + 2)$

Use the Principle of Mathematical Induction to prove that for all $n \in N$:
$\cos \alpha + \cos (\alpha + \beta) + \cos (\alpha + 2\beta) + \ldots + \cos [\alpha + (n-1)\beta] = \frac{\cos \left[\alpha + \left(\frac{n-1}{2}\right) \beta\right] \sin \left(\frac{n\beta}{2}\right)}{\sin \left(\frac{\beta}{2}\right)}$

Let $P(n)$ be a statement and let $P(n) \implies P(n + 1)$ for all natural numbers $n$. Then $P(n)$ is true for:

Prove the following by using the principle of mathematical induction for all $n \in N$:
$\frac{1}{3 \times 5} + \frac{1}{5 \times 7} + \frac{1}{7 \times 9} + \ldots + \frac{1}{(2n+1)(2n+3)} = \frac{n}{3(2n+3)}$