Let P (n) be the statement that 1^3+2^3+...+n^3=\left(n\frac{(n+1)}{2}\right)

gainejavima

gainejavima

Answered question

2021-11-10

Let P (n) be the statement that 13+23++n3=(n(n+1)2)2 for the positive integer n. 

a) What is the statement P (1)? 

b) Show that P (1) is true, completing the basis step of the proof. 

c) What is the inductive hypothesis? 

d) What do you need to prove in the inductive step? 

e) Complete the inductive step, identifying where you use the inductive hypothesis. 

f ) Explain why these steps show that this formula is true whenever n is a positive integer.

Answer & Explanation

James Obrien

James Obrien

Beginner2021-11-11Added 16 answers

a)  P(1):13=(1(1+1)2)2


b) for  η=1
13=(22)2
1=12=1QED


c) Assume  P(k)  for  k1:13+23++k3=(k(k+1)2)2


d)  P(k+1):


e) ((k+1)((k+1)+1)2)2=13+23++k3+(k+1)3
((k+1)((k+1)+1)2)2=(k(k+1)2)+(k+1)3
((k+1)(k+2)2)2=(k2+k2)+4(k+1)34
(k+1)(k+2)2(k+1)(k+2)2=k2+k2k2+k2+4(k+1)34
k4+6k3+13k2+12k+44=k4+2k3+k2+4k3+12k2+45
k4+6k3+13k2+12k+44=k4+6k3+13k2+12k+44

f) 1. P(b)for constant b
2.kb(P(k)P(k+1))

Nick Camelot

Nick Camelot

Skilled2023-05-25Added 164 answers

Step 1:
a) The statement P(1) is:
P(1): 13=(1(1+1)2)2
Step 2:
b) To show that P(1) is true, we substitute the values and simplify both sides of the equation:
13=(1(1+1)2)2
1=(22)2
1=12
Since the equation is true, P(1) is true.
Step 3:
c) The inductive hypothesis is:
P(k): 13+23+...+k3=(k(k+1)2)2
Step 4:
d) In the inductive step, we need to prove that if P(k) is true, then P(k+1) is also true. In other words, we assume the equation holds for a particular value of k and then use it to show that it holds for the next value (k+1).
Step 5:
e) Let's assume that P(k) is true for some positive integer k. That is:
P(k): 13+23+...+k3=(k(k+1)2)2
Now we need to prove that P(k+1) is true, which means:
P(k+1): 13+23+...+k3+(k+1)3=((k+1)((k+1)+1)2)2
To prove this, we start with the left-hand side (LHS) of P(k+1) and use the inductive hypothesis:
13+23+...+k3+(k+1)3
=(k(k+1)2)2+(k+1)3
=k2(k+1)24+(k+1)3
=k2(k+1)2+4(k+1)34
=(k+1)2(k2+4(k+1))4
=(k+1)2(k2+4k+4)4
=(k+1)2(k+2)24
=((k+1)(k+2)2)2
=((k+1)((k+1)+1)2)2
=((k+1)(k+2)2)2
Therefore, we have shown that P(k+1) holds true based on the assumption that P(k) is true. This completes the inductive step.
Step 6:
f) The steps above demonstrate that P(1) is true (basis step) and that if P(k) is true, then P(k+1) is also true (inductive step). By following these steps repeatedly, starting from the basis step and applying the inductive step, we can prove that the equation 13+23+...+n3=(n(n+1)2)2 holds true for any positive integer n.
Mr Solver

Mr Solver

Skilled2023-05-25Added 147 answers

a) P(1): 13=(1((1+1))2)2
b) To show that P(1) is true, we substitute n=1 into the equation and simplify:
13=(1((1+1))2)2
1=(1(2)2)2
1=(22)2
1=12
Thus, P(1) is true.
c) The inductive hypothesis is that for some positive integer k, P(k) is true. In other words, we assume that 13+23+...+k3=(k((k+1))2)2 is true.
d) In the inductive step, we need to prove that if P(k) is true, then P(k+1) is also true. We need to show that 13+23+...+k3+(k+1)3=((k+1)((k+1)+1)2)2 holds.
e) To complete the inductive step, we assume that P(k) is true, which means:
13+23+...+k3=(k((k+1))2)2
Then, we add (k+1)3 to both sides of the equation:
13+23+...+k3+(k+1)3=(k((k+1))2)2+(k+1)3
Expanding and simplifying the right side:
(k2(k+1)24)+(k+1)3
Factoring out (k+1)2:
(k+1)2(k24+(k+1))
Simplifying (k24+(k+1)):
(k24+4(k+1)4)
(k2+4k+44)
((k+2)24)
Substituting back into the equation:
13+23+...+k3+(k+1)3=((k+1)((k+1)+1)2)2
(k+1)2((k+2)24)=((k+1)(k+2)2)2
(k+1)2((k+2)24)=((k+1)(k+2)2)2
Thus, using the inductive hypothesis, we have shown that P(k+1) is true.
f) By completing the basis step and the inductive step, we have shown that P(n) is true for any positive integer n. This means that the formula 13+23+...+n3=(n((n+1))2)2
holds whenever n is a positive integer.

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