Number and Algebra
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Prove by induction that the sum of the first nnn odd numbers is 1+3+5+⋯+(2n−1)=n21 + 3 + 5 + \dots + (2n-1) = n^21+3+5+⋯+(2n−1)=n2.
Consider the sequence defined by a1=2a_1=2a1=2 and an=an−1+3for n≥2.a_n=a_{n-1}+3\quad\text{for }n\ge2\text{.}an=an−1+3for n≥2. Prove by induction that an=3n−1for all n≥1.a_n=3n-1\quad\text{for all }n\ge1\text{.}an=3n−1for all n≥1.
Prove by induction that 12+22+⋯+n2=n(n+1)(2n+1)61^2 + 2^2 + \dots + n^2 = \frac{n(n+1)(2n+1)}{6} 12+22+⋯+n2=6n(n+1)(2n+1).
Prove by induction that 13+23+⋯+n3=(n(n+1)2)21^3 + 2^3 + \dots + n^3 = \left(\frac{n(n+1)}{2}\right)^213+23+⋯+n3=(2n(n+1))2.
Verify by induction that 1+2+3+⋯+n=n(n+1)21 + 2 + 3 + \dots + n = \frac{n(n+1)}{2}1+2+3+⋯+n=2n(n+1) for all positive integers nnn.
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