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(a) Use the principle of mathematical induction to show that for all integers 
n >= 1,
1×2+2×5+3×8+cdots+n(3n-1)=n^(2)(n+1).

(a) Use the principle of mathematical induction to show that for all integers n1n \geq 1, 1×2+2×5+3×8++n(3n1)=n2(n+1).1\times2+2\times5+3\times8+\cdots+n(3n-1)=n^{2}(n+1).

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Q. (a) Use the principle of mathematical induction to show that for all integers n1n \geq 1, 1×2+2×5+3×8++n(3n1)=n2(n+1).1\times2+2\times5+3\times8+\cdots+n(3n-1)=n^{2}(n+1).
  1. State Proposition P(n)P(n): State the proposition P(n)P(n) that we want to prove using mathematical induction.\newlineP(n)P(n): 1×2+2×5+3×8++n(3n1)=n2(n+1)1\times2 + 2\times5 + 3\times8 + \ldots + n(3n-1) = n^2(n+1)
  2. Verify Base Case: Verify the base case, P(1)P(1), to ensure it holds true.\newlineFor n=1n = 1, the left-hand side of the equation is 1×2=21\times2 = 2.\newlineThe right-hand side of the equation is 12(1+1)=1×2=21^2(1+1) = 1\times2 = 2.\newlineSince both sides are equal, P(1)P(1) is true.
  3. Assume Induction Hypothesis: Assume that P(k)P(k) is true for some positive integer kk, where k1k \geq 1. This is the induction hypothesis.\newlineAssume 1×2+2×5+3×8++k(3k1)=k2(k+1)1\times2 + 2\times5 + 3\times8 + \ldots + k(3k-1) = k^2(k+1)
  4. Show Implication for P(k+1)P(k+1): Show that P(k)P(k) being true implies that P(k+1)P(k+1) is also true.\newlineWe need to prove that 1×2+2×5+3×8++k(3k1)+(k+1)(3(k+1)1)=(k+1)2(k+2)1\times2 + 2\times5 + 3\times8 + \ldots + k(3k-1) + (k+1)(3(k+1)-1) = (k+1)^2(k+2)
  5. Simplify Left-hand Side: Start with the left-hand side of P(k+1)P(k+1) and use the induction hypothesis to simplify.1×2+2×5+3×8++k(3k1)+(k+1)(3(k+1)1)1\times 2 + 2\times 5 + 3\times 8 + \ldots + k(3k-1) + (k+1)(3(k+1)-1)=k2(k+1)+(k+1)(3k+31) [Using the induction hypothesis]= k^2(k+1) + (k+1)(3k+3-1) \text{ [Using the induction hypothesis]}=k2(k+1)+(k+1)(3k+2)= k^2(k+1) + (k+1)(3k+2)
  6. Expand and Simplify: Expand and simplify the expression.\newline=k3+k2+3k2+6k+2k+2= k^3 + k^2 + 3k^2 + 6k + 2k + 2\newline=k3+4k2+8k+2= k^3 + 4k^2 + 8k + 2
  7. Factor Expression: Factor the expression to match the right-hand side of P(k+1)P(k+1). \newline= (k+1)2(k+2)(k+1)^2(k+2)
  8. Verify Equality: Verify that the right-hand side of P(k+1)P(k+1) matches the simplified left-hand side.\newlineSince both sides are equal, P(k+1)P(k+1) is true whenever P(k)P(k) is true.
  9. Conclude by Induction: Conclude the proof by mathematical induction. Since P(1)P(1) is true and P(k)P(k) implies P(k+1)P(k+1), by the principle of mathematical induction, P(n)P(n) is true for all integers n1n \geq 1.

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