Concept explainers
To proof: The expression 3+5+7+⋯+(2n+1)=n(n+2) with help of mathematical induction for integers n≥1 .

Explanation of Solution
Given information:
The expression 3+5+7+⋯+(2n+1)=n(n+2) .
Formula used:
The steps to prove a statement by mathematical induction are as follows:
Step 1. Show that the statement is true for n=1 .
Step 2. Assume that the statement is true for n=k .
Step 3. Prove that the statement is true for n=k+1 with help of step 2.
Proof:
Consider expression 3+5+7+⋯+(2n+1)=n(n+2) .
Denote the expression by Sn .
Recall that the steps to prove a statement by mathematical induction are as follows:
Step 1. Show that the statement is true for n=1 .
Step 2. Assume that the statement is true for n=k .
Step 3. Prove that the statement is true for n=k+1 with help of step 2.
Substitute n=1 in the expression,
2(1)+1=1(1+2)3=3
The above equation holds true.
Therefore, the statement is true for n=1 so S1 is true.
Now, assume that the statement if true for n=k .
3+5+7+⋯+(2k+1)=k(k+2)
...(1)
Therefore, the statement holds true for n=k so Sk is true.
Now, prove it for n=k+1 . Write the expression for n=k+1 . Group the terms that involve Sk .
3+5+7+⋯+(2k+1)+[2(k+1)+1]=Sk+[2(k+1)+1]
Substitute the value of Sk from equation (1),
3+5+7+⋯+(2k+1)+[2(k+1)+1]=Sk+[2(k+1)+1]=k(k+2)+[2(k+1)+1]=k2+2k+2k+3=k2+4k+3
Factor out the terms and simplify,
3+5+7+⋯+(2k+1)+[2(k+1)+1]=k2+3k+k+3=k(k+3)+1(k+3)=(k+1)(k+3)=(k+1)[(k+1)+2]
Result obtained is that Sk implies Sk+1 that is,
3+5+7+⋯+(2k+1)+[2(k+1)+1]=(k+1)[(k+1)+2]
Hence, by the principle of mathematical induction the statement 3+5+7+⋯+(2n+1)=n(n+2) is true for all integers n≥1 .
Chapter 9 Solutions
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