Baka to Tesuto to Syokanju:Volume7 The Fourth Question
Use mathematical induction [1]
to prove the following:
1 + 3 + 5 + … + (2n-1)=n2 – (1)
- When n is a natural number.
Himeji Mizuki's answer
1. When n=1, equation (1) is calculated as,
- Left Hand Side = 1
- Right Hand Side = 1
2. Assuming that n=k is valid,
- 1 + 3 + 5 + … + (2k-1)=k2 - (2)
- When n=k+1, the left hand side of (1) is written as
- 1 + 3 + 5 + … + (2k-1)+(2k+1)
- =k2 + (2k+1) (Obtained from equation (2))
- =(k+1)2
In other words,
- 1 + 3 + 5 + … + (2k-1)+(2k+1)
- =(k+1)2
(1) is valid when n=k+1.
From both equations (1) and (2), equation (1) is valid for all values on n.
Teacher's comment
That's correct. In mathematical induction, you need to prove that n=1 is valid. Also, when assuming that n=k is valid, you have to deduce that n=k+1 is valid. In this question, the key is that n is a natural number. On a side note, people often forget to put that n=1, so do take note when answering.
Tsuchiya Kouta's answer
"I'll prove here that (1) is correct - Tsuchiya Kouta"
Teacher's comment
Even if you try to sneak through by writing it in a style of a thesis, it's usless. The question mentioned that you have to prove it through 'mathematical induction', so while assuming that n=k, please write the equation that n=k+1 is valid.
Yoshii Akihisa's answer
"My judgment can hold."
Teacher's comment
"Please use an assumption."