EAPCET Mathematics · Intermediate first year · Paper IA

Mathematical Induction

Mathematical induction proves that a statement holds for every natural number by checking a first case and showing each case implies the next. In EAPCET it mostly appears through summation and divisibility results.

Subject
Mathematics
Taught in
Intermediate first year · Paper IA
Mathematics in the paper
80 of 160 questions

Key formulas and results

  • If P(1)P(1) is true and P(k)⇒P(k+1)P(k) \Rightarrow P(k + 1), then P(n)P(n) is true for all natural numbers nn.
  • 1+2+⋯+n=n(n+1)21 + 2 + \dots + n = \dfrac{n(n + 1)}{2}
  • 12+22+⋯+n2=n(n+1)(2n+1)61^{2} + 2^{2} + \dots + n^{2} = \dfrac{n(n + 1)(2n + 1)}{6}
  • 13+23+⋯+n3=[n(n+1)2]21^{3} + 2^{3} + \dots + n^{3} = \left[\dfrac{n(n + 1)}{2}\right]^{2}
  • an−bna^{n} - b^{n} is divisible by a−ba - b for every natural number nn.

What this chapter covers

  • Principle of mathematical induction
  • Proving summation formulas
  • Divisibility statements
  • Inequalities involving natural numbers

How it is usually asked

  • Find the sum of a series using the standard sums
  • Find the number a given expression is always divisible by
  • Identify the correct closed form for a series

Understanding Mathematical Induction

Mathematical induction proves that a statement P(n) is true for every natural number n in two steps. First, check the base case P(1) directly. Second, assume P(k) is true for an arbitrary k and use that assumption to prove P(k + 1). Like a row of dominoes, the first case is true and each case pushes over the next, so the statement holds for all n.

The inductive step is where the work lies. For a summation formula, you add the (k + 1)th term to both sides of P(k) and simplify the right side into the formula with k replaced by k + 1. For a divisibility statement, you rewrite the (k + 1) expression so that it contains the k expression, which is divisible by assumption, plus a part that is clearly divisible.

In EAPCET the method itself is rarely asked as a full proof. Instead you are given a series or an expression in n and asked for its closed form or a number that always divides it. Two tools solve almost all of these: the standard sums of n, n² and n³, and substituting small values like n = 1 and n = 2 into the options to eliminate the wrong ones.

Worked example

EAPCET-style question

For every natural number nn, 1⋅2+2⋅3+3⋅4+⋯+n(n+1)1 \cdot 2 + 2 \cdot 3 + 3 \cdot 4 + \dots + n(n + 1) equals

  1. (1)n(n+1)(n+2)3\dfrac{n(n + 1)(n + 2)}{3}
  2. (2)n(n+1)(n+2)6\dfrac{n(n + 1)(n + 2)}{6}
  3. (3)n(n+1)(2n+1)6\dfrac{n(n + 1)(2n + 1)}{6}
  4. (4)n2(n+1)2\dfrac{n^{2}(n + 1)}{2}

Solution

  1. Write the general term as k(k+1)=k2+kk(k + 1) = k^{2} + k.
  2. So the sum =∑k2+∑k=n(n+1)(2n+1)6+n(n+1)2= \sum k^{2} + \sum k = \dfrac{n(n + 1)(2n + 1)}{6} + \dfrac{n(n + 1)}{2}.
  3. Take n(n+1)6\dfrac{n(n + 1)}{6} common: n(n+1)[(2n+1)+3]6=n(n+1)(2n+4)6\dfrac{n(n + 1)[(2n + 1) + 3]}{6} = \dfrac{n(n + 1)(2n + 4)}{6}.
  4. Simplify to n(n+1)(n+2)3\dfrac{n(n + 1)(n + 2)}{3}.
  5. Check: n=1n = 1 gives 2 and n=2n = 2 gives 2+6=82 + 6 = 8; only the first option gives both.

Answer: n(n+1)(n+2)3\dfrac{n(n + 1)(n + 2)}{3}

Common mistakes to avoid

  • Testing an option only at n = 1, where several options often agree; always check n = 2 as well before choosing.
  • Using [n(n + 1)/2]² for the sum of squares; that is the sum of cubes, while the sum of squares is n(n + 1)(2n + 1)/6.
  • In the inductive step, adding k + 1 instead of the actual (k + 1)th term; substitute k + 1 into the general term of the series.
  • For “divisible by” questions, picking a large divisor that works for n = 1 but not n = 2; the answer must divide every value, so test two cases.

How to prepare it

In a multiple-choice question you rarely need the full proof: substitute n = 1 and n = 2 into each option and eliminate the ones that fail.

Memorise the three standard sums — most questions reduce to them.

Once the formulas feel familiar, test them the way the exam does: practise Mathematical Induction questions chapter-wise, then attempt a full previous year paper to see whether it holds up under a 3-hour timer.

Related Mathematics chapters

See every chapter in the EAPCET Mathematics syllabus.

Practise Mathematical Induction chapter-wise

Chapter-wise quizzes show exactly which topics in this chapter you still get wrong — before a full paper does.

Frequently asked questions

Is Mathematical Induction part of the EAPCET Mathematics syllabus?
Yes. Mathematical Induction is taught in Intermediate first year · Paper IA Mathematics, and the EAPCET Engineering syllabus is based on the Intermediate first- and second-year syllabus. Check the official notification each year for any changes.
How should I prepare Mathematical Induction for EAPCET?
In a multiple-choice question you rarely need the full proof: substitute n = 1 and n = 2 into each option and eliminate the ones that fail. Memorise the three standard sums — most questions reduce to them.
How many Mathematics questions are there in EAPCET?
80 of the 160 questions in the Engineering paper are Mathematics, spread across 37 chapters.
What mistakes do students make in Mathematical Induction?
Testing an option only at n = 1, where several options often agree; always check n = 2 as well before choosing. Using [n(n + 1)/2]² for the sum of squares; that is the sum of cubes, while the sum of squares is n(n + 1)(2n + 1)/6. In the inductive step, adding k + 1 instead of the actual (k + 1)th term; substitute k + 1 into the general term of the series. For “divisible by” questions, picking a large divisor that works for n = 1 but not n = 2; the answer must divide every value, so test two cases.