Q. (a) Use the principle of mathematical induction to show that for all integers n≥1, 1×2+2×5+3×8+⋯+n(3n−1)=n2(n+1).
State Proposition P(n): State the proposition P(n) that we want to prove using mathematical induction.P(n): 1×2+2×5+3×8+…+n(3n−1)=n2(n+1)
Verify Base Case: Verify the base case, P(1), to ensure it holds true.For n=1, the left-hand side of the equation is 1×2=2.The right-hand side of the equation is 12(1+1)=1×2=2.Since both sides are equal, P(1) is true.
Assume Induction Hypothesis: Assume that P(k) is true for some positive integer k, where k≥1. This is the induction hypothesis.Assume 1×2+2×5+3×8+…+k(3k−1)=k2(k+1)
Show Implication for P(k+1): Show that P(k) being true implies that P(k+1) is also true.We need to prove that 1×2+2×5+3×8+…+k(3k−1)+(k+1)(3(k+1)−1)=(k+1)2(k+2)
Simplify Left-hand Side: Start with the left-hand side of P(k+1) and use the induction hypothesis to simplify.1×2+2×5+3×8+…+k(3k−1)+(k+1)(3(k+1)−1)=k2(k+1)+(k+1)(3k+3−1) [Using the induction hypothesis]=k2(k+1)+(k+1)(3k+2)
Expand and Simplify: Expand and simplify the expression.=k3+k2+3k2+6k+2k+2=k3+4k2+8k+2
Factor Expression: Factor the expression to match the right-hand side of P(k+1). = (k+1)2(k+2)
Verify Equality: Verify that the right-hand side of P(k+1) matches the simplified left-hand side.Since both sides are equal, P(k+1) is true whenever P(k) is true.
Conclude by Induction: Conclude the proof by mathematical induction. Since P(1) is true and P(k) implies P(k+1), by the principle of mathematical induction, P(n) is true for all integers n≥1.
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