Why is this equality wrong? Can't find a proof
$begingroup$
I can't understant why these two formulas are not equal, I am certain they are but I cannot find a proof for my claim:
$$sum_{i=0}^{x-1} 2^{i} = 2^x-1$$
Edit: They are equal, thanks for the help
linear-algebra summation proof-explanation equivalence-relations
New contributor
Jack Möller is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
add a comment |
$begingroup$
I can't understant why these two formulas are not equal, I am certain they are but I cannot find a proof for my claim:
$$sum_{i=0}^{x-1} 2^{i} = 2^x-1$$
Edit: They are equal, thanks for the help
linear-algebra summation proof-explanation equivalence-relations
New contributor
Jack Möller is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
3
$begingroup$
Prove by induction on $xgeq 1$.
$endgroup$
– Wuestenfux
1 hour ago
$begingroup$
Did you really mean to say "(...) are not equal, I am certain they are"?
$endgroup$
– StackTD
1 hour ago
$begingroup$
Multiply the left hand side by $(2-1)$ using the distributive law, simplify.
$endgroup$
– Ned
1 hour ago
$begingroup$
If you are familiar with geometric progressions, you could also use $sum_limits{i = 0}^{x-1} u_1r^i = frac{u_1left(1-r^xright)}{1-r}$.
$endgroup$
– KM101
1 hour ago
add a comment |
$begingroup$
I can't understant why these two formulas are not equal, I am certain they are but I cannot find a proof for my claim:
$$sum_{i=0}^{x-1} 2^{i} = 2^x-1$$
Edit: They are equal, thanks for the help
linear-algebra summation proof-explanation equivalence-relations
New contributor
Jack Möller is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
I can't understant why these two formulas are not equal, I am certain they are but I cannot find a proof for my claim:
$$sum_{i=0}^{x-1} 2^{i} = 2^x-1$$
Edit: They are equal, thanks for the help
linear-algebra summation proof-explanation equivalence-relations
linear-algebra summation proof-explanation equivalence-relations
New contributor
Jack Möller is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
Jack Möller is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited 1 hour ago
Jack Möller
New contributor
Jack Möller is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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asked 1 hour ago
Jack MöllerJack Möller
62
62
New contributor
Jack Möller is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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New contributor
Jack Möller is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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Jack Möller is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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3
$begingroup$
Prove by induction on $xgeq 1$.
$endgroup$
– Wuestenfux
1 hour ago
$begingroup$
Did you really mean to say "(...) are not equal, I am certain they are"?
$endgroup$
– StackTD
1 hour ago
$begingroup$
Multiply the left hand side by $(2-1)$ using the distributive law, simplify.
$endgroup$
– Ned
1 hour ago
$begingroup$
If you are familiar with geometric progressions, you could also use $sum_limits{i = 0}^{x-1} u_1r^i = frac{u_1left(1-r^xright)}{1-r}$.
$endgroup$
– KM101
1 hour ago
add a comment |
3
$begingroup$
Prove by induction on $xgeq 1$.
$endgroup$
– Wuestenfux
1 hour ago
$begingroup$
Did you really mean to say "(...) are not equal, I am certain they are"?
$endgroup$
– StackTD
1 hour ago
$begingroup$
Multiply the left hand side by $(2-1)$ using the distributive law, simplify.
$endgroup$
– Ned
1 hour ago
$begingroup$
If you are familiar with geometric progressions, you could also use $sum_limits{i = 0}^{x-1} u_1r^i = frac{u_1left(1-r^xright)}{1-r}$.
$endgroup$
– KM101
1 hour ago
3
3
$begingroup$
Prove by induction on $xgeq 1$.
$endgroup$
– Wuestenfux
1 hour ago
$begingroup$
Prove by induction on $xgeq 1$.
$endgroup$
– Wuestenfux
1 hour ago
$begingroup$
Did you really mean to say "(...) are not equal, I am certain they are"?
$endgroup$
– StackTD
1 hour ago
$begingroup$
Did you really mean to say "(...) are not equal, I am certain they are"?
$endgroup$
– StackTD
1 hour ago
$begingroup$
Multiply the left hand side by $(2-1)$ using the distributive law, simplify.
$endgroup$
– Ned
1 hour ago
$begingroup$
Multiply the left hand side by $(2-1)$ using the distributive law, simplify.
$endgroup$
– Ned
1 hour ago
$begingroup$
If you are familiar with geometric progressions, you could also use $sum_limits{i = 0}^{x-1} u_1r^i = frac{u_1left(1-r^xright)}{1-r}$.
$endgroup$
– KM101
1 hour ago
$begingroup$
If you are familiar with geometric progressions, you could also use $sum_limits{i = 0}^{x-1} u_1r^i = frac{u_1left(1-r^xright)}{1-r}$.
$endgroup$
– KM101
1 hour ago
add a comment |
5 Answers
5
active
oldest
votes
$begingroup$
$$
S(x) = sum_{i=0}^{x-1} 2^{i} \
2 S(x) = 2 sum_{i=0}^{x-1} 2^{i} = sum_{i=0}^{x-1} 2^{i+1} = sum_{k=1}^{x} 2^{k} = S(x) + 2^x - 1
$$
so this is your proof that indeed $ S(x) = 2^x - 1 $.
$endgroup$
add a comment |
$begingroup$
The easiest way is to notice that
$$
sum_{i=0}^{x-1}2^i=sum_{i=0}^{x-1}(2^{i+1}-2^{i})=({2^1}-2^0)+(2^2-2^1)+(2^3-2^2)+dotsb+(2^x-2^{x-1})
$$
which is a telescoping series.
$endgroup$
add a comment |
$begingroup$
Use induction to prove it:
Show it is true for $x=1$
Assume it is true for $x=k$, this means that you are allowed to use $$sum_{i=0}^{k-1} 2^{i} = 2^k-1$$
Then show that it is true for $n=k+1$ by using the above formula.
$endgroup$
add a comment |
$begingroup$
You can prove this equality with the following method:
x belongs to N*
For x=1, 2^0 = 2^1 - 1 = 1
For x=2, 2^0 + 2^1 = 2^2 - 1 = 3
.
.
.
Assume that the equality is correct up to (x-1) and demonstrate for the next order (see attached image),
Proof
Thus, the equality holds for all x in N*
New contributor
Wane Mamadou is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
add a comment |
$begingroup$
Applying the finite geometric series formula we obtain
begin{align*}
sum_{i=0}^{x-1}2^i=frac{2^x-1}{2-1}=2^x-1
end{align*}
$endgroup$
add a comment |
Your Answer
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5 Answers
5
active
oldest
votes
5 Answers
5
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
$$
S(x) = sum_{i=0}^{x-1} 2^{i} \
2 S(x) = 2 sum_{i=0}^{x-1} 2^{i} = sum_{i=0}^{x-1} 2^{i+1} = sum_{k=1}^{x} 2^{k} = S(x) + 2^x - 1
$$
so this is your proof that indeed $ S(x) = 2^x - 1 $.
$endgroup$
add a comment |
$begingroup$
$$
S(x) = sum_{i=0}^{x-1} 2^{i} \
2 S(x) = 2 sum_{i=0}^{x-1} 2^{i} = sum_{i=0}^{x-1} 2^{i+1} = sum_{k=1}^{x} 2^{k} = S(x) + 2^x - 1
$$
so this is your proof that indeed $ S(x) = 2^x - 1 $.
$endgroup$
add a comment |
$begingroup$
$$
S(x) = sum_{i=0}^{x-1} 2^{i} \
2 S(x) = 2 sum_{i=0}^{x-1} 2^{i} = sum_{i=0}^{x-1} 2^{i+1} = sum_{k=1}^{x} 2^{k} = S(x) + 2^x - 1
$$
so this is your proof that indeed $ S(x) = 2^x - 1 $.
$endgroup$
$$
S(x) = sum_{i=0}^{x-1} 2^{i} \
2 S(x) = 2 sum_{i=0}^{x-1} 2^{i} = sum_{i=0}^{x-1} 2^{i+1} = sum_{k=1}^{x} 2^{k} = S(x) + 2^x - 1
$$
so this is your proof that indeed $ S(x) = 2^x - 1 $.
edited 58 mins ago
answered 1 hour ago
AndreasAndreas
7,8581037
7,8581037
add a comment |
add a comment |
$begingroup$
The easiest way is to notice that
$$
sum_{i=0}^{x-1}2^i=sum_{i=0}^{x-1}(2^{i+1}-2^{i})=({2^1}-2^0)+(2^2-2^1)+(2^3-2^2)+dotsb+(2^x-2^{x-1})
$$
which is a telescoping series.
$endgroup$
add a comment |
$begingroup$
The easiest way is to notice that
$$
sum_{i=0}^{x-1}2^i=sum_{i=0}^{x-1}(2^{i+1}-2^{i})=({2^1}-2^0)+(2^2-2^1)+(2^3-2^2)+dotsb+(2^x-2^{x-1})
$$
which is a telescoping series.
$endgroup$
add a comment |
$begingroup$
The easiest way is to notice that
$$
sum_{i=0}^{x-1}2^i=sum_{i=0}^{x-1}(2^{i+1}-2^{i})=({2^1}-2^0)+(2^2-2^1)+(2^3-2^2)+dotsb+(2^x-2^{x-1})
$$
which is a telescoping series.
$endgroup$
The easiest way is to notice that
$$
sum_{i=0}^{x-1}2^i=sum_{i=0}^{x-1}(2^{i+1}-2^{i})=({2^1}-2^0)+(2^2-2^1)+(2^3-2^2)+dotsb+(2^x-2^{x-1})
$$
which is a telescoping series.
answered 1 hour ago
Foobaz JohnFoobaz John
21.7k41352
21.7k41352
add a comment |
add a comment |
$begingroup$
Use induction to prove it:
Show it is true for $x=1$
Assume it is true for $x=k$, this means that you are allowed to use $$sum_{i=0}^{k-1} 2^{i} = 2^k-1$$
Then show that it is true for $n=k+1$ by using the above formula.
$endgroup$
add a comment |
$begingroup$
Use induction to prove it:
Show it is true for $x=1$
Assume it is true for $x=k$, this means that you are allowed to use $$sum_{i=0}^{k-1} 2^{i} = 2^k-1$$
Then show that it is true for $n=k+1$ by using the above formula.
$endgroup$
add a comment |
$begingroup$
Use induction to prove it:
Show it is true for $x=1$
Assume it is true for $x=k$, this means that you are allowed to use $$sum_{i=0}^{k-1} 2^{i} = 2^k-1$$
Then show that it is true for $n=k+1$ by using the above formula.
$endgroup$
Use induction to prove it:
Show it is true for $x=1$
Assume it is true for $x=k$, this means that you are allowed to use $$sum_{i=0}^{k-1} 2^{i} = 2^k-1$$
Then show that it is true for $n=k+1$ by using the above formula.
answered 1 hour ago
Ben CrossleyBen Crossley
787318
787318
add a comment |
add a comment |
$begingroup$
You can prove this equality with the following method:
x belongs to N*
For x=1, 2^0 = 2^1 - 1 = 1
For x=2, 2^0 + 2^1 = 2^2 - 1 = 3
.
.
.
Assume that the equality is correct up to (x-1) and demonstrate for the next order (see attached image),
Proof
Thus, the equality holds for all x in N*
New contributor
Wane Mamadou is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
add a comment |
$begingroup$
You can prove this equality with the following method:
x belongs to N*
For x=1, 2^0 = 2^1 - 1 = 1
For x=2, 2^0 + 2^1 = 2^2 - 1 = 3
.
.
.
Assume that the equality is correct up to (x-1) and demonstrate for the next order (see attached image),
Proof
Thus, the equality holds for all x in N*
New contributor
Wane Mamadou is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
add a comment |
$begingroup$
You can prove this equality with the following method:
x belongs to N*
For x=1, 2^0 = 2^1 - 1 = 1
For x=2, 2^0 + 2^1 = 2^2 - 1 = 3
.
.
.
Assume that the equality is correct up to (x-1) and demonstrate for the next order (see attached image),
Proof
Thus, the equality holds for all x in N*
New contributor
Wane Mamadou is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
You can prove this equality with the following method:
x belongs to N*
For x=1, 2^0 = 2^1 - 1 = 1
For x=2, 2^0 + 2^1 = 2^2 - 1 = 3
.
.
.
Assume that the equality is correct up to (x-1) and demonstrate for the next order (see attached image),
Proof
Thus, the equality holds for all x in N*
New contributor
Wane Mamadou is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
Wane Mamadou is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
answered 1 hour ago
Wane MamadouWane Mamadou
1
1
New contributor
Wane Mamadou is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
Wane Mamadou is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Wane Mamadou is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
add a comment |
add a comment |
$begingroup$
Applying the finite geometric series formula we obtain
begin{align*}
sum_{i=0}^{x-1}2^i=frac{2^x-1}{2-1}=2^x-1
end{align*}
$endgroup$
add a comment |
$begingroup$
Applying the finite geometric series formula we obtain
begin{align*}
sum_{i=0}^{x-1}2^i=frac{2^x-1}{2-1}=2^x-1
end{align*}
$endgroup$
add a comment |
$begingroup$
Applying the finite geometric series formula we obtain
begin{align*}
sum_{i=0}^{x-1}2^i=frac{2^x-1}{2-1}=2^x-1
end{align*}
$endgroup$
Applying the finite geometric series formula we obtain
begin{align*}
sum_{i=0}^{x-1}2^i=frac{2^x-1}{2-1}=2^x-1
end{align*}
answered 10 mins ago
Markus ScheuerMarkus Scheuer
60.6k455145
60.6k455145
add a comment |
add a comment |
Jack Möller is a new contributor. Be nice, and check out our Code of Conduct.
Jack Möller is a new contributor. Be nice, and check out our Code of Conduct.
Jack Möller is a new contributor. Be nice, and check out our Code of Conduct.
Jack Möller is a new contributor. Be nice, and check out our Code of Conduct.
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3
$begingroup$
Prove by induction on $xgeq 1$.
$endgroup$
– Wuestenfux
1 hour ago
$begingroup$
Did you really mean to say "(...) are not equal, I am certain they are"?
$endgroup$
– StackTD
1 hour ago
$begingroup$
Multiply the left hand side by $(2-1)$ using the distributive law, simplify.
$endgroup$
– Ned
1 hour ago
$begingroup$
If you are familiar with geometric progressions, you could also use $sum_limits{i = 0}^{x-1} u_1r^i = frac{u_1left(1-r^xright)}{1-r}$.
$endgroup$
– KM101
1 hour ago