गणितीय आगमन के सिद्धांत में निम्नलिखित में से कौन सा चरण अनिवार्य है?

How does Strong Induction (often referred to as the Second/Third Principle of Induction) differ from Weak Induction (First Principle of Induction)?

For every natural number n ≥ 2, if P(n) = √n and Q(n) = 1√1 + 1√2 + 1√3 + ... + 1√n, then which inequality holds true?