Problem 1
Use mathematical induction to prove that
1 + 2 + 3 + ... + n = n (n + 1) / 2
for all positive integers n.
Answers
Solution to Problem 1:
Let the statement P (n) be
1 + 2 + 3 + ... + n = n (n + 1) / 2
STEP 1: We first show that p (1) is true.
Left Side = 1
Right Side = 1 (1 + 1) / 2 = 1
Both sides of the statement are equal hence p (1) is true.
STEP 2: We now assume that p (k) is true
1 + 2 + 3 + ... + k = k (k + 1) / 2
and show that p (k + 1) is true by adding k + 1 to both sides of the above statement
1 + 2 + 3 + ... + k + (k + 1) = k (k + 1) / 2 + (k + 1)
= (k + 1)(k / 2 + 1)
= (k + 1)(k + 2) / 2
The last statement may be written as
1 + 2 + 3 + ... + k + (k + 1) = (k + 1)(k + 2) / 2
Which is the statement p(k + 1).
Answer:
STEP 1: Show that the statement is true for n = 1
1 = 1 (1 + 1) /2
1 = 1 (2) /2
1 = 1
STEP 2: Assume that the statement is true for some positive integer K.
Assume that 1 + 2 + 3 + .... + k = k (k + 1) /2
STEP 3: Show that the statement is true for the next positive integer K + 1.
1 + 2 + 3 + ... + K + (k + 1) =
k (k + 1) /2 + (k + 1) Induction Hypothesis.
= k (k + 1) + 2 (k + 1) /2 add
= (k + 1) (k + 2) /2 simplify
= (k + 1) [ (k + 1) + 1 ] /2 k + 2 = (k + 1) + 1
Because the statement is true for n = 1 and
1 + 2 + 3 + ... + K + (K + 1) = (k + 1) [ (K + 1) + 1 ] /2,
1 + 2 + 3+ ..... + n = n(n + 1) /2 is true for all positive integers n.
Step-by-step explanation:
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