These Numerators Diverge Too

Algebra Level 3

True or False?

1 0 ! + 1 1 ! + 1 2 ! + 1 3 ! + 1 4 ! + = 0 0 ! + 1 1 ! + 2 2 ! + 3 3 ! + 4 4 ! + \dfrac1{0!} + \dfrac1{1!} + \dfrac1{2!} + \dfrac1{3!} + \dfrac1{4!} + \cdots = \dfrac0{0!} + \dfrac1{1!} + \dfrac2{2!} + \dfrac3{3!} + \dfrac4{4!} + \cdots

Notation : ! ! denotes the factorial notation. For example, 8 ! = 1 × 2 × 3 × × 8 8! = 1\times2\times3\times\cdots\times8 .

True False

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2 solutions

Bloons Qoth
Aug 25, 2016

So 0 0 ! + 1 1 ! + 2 2 ! + 3 3 ! + 4 4 ! + \dfrac0{0!} + \dfrac1{1!} + \dfrac2{2!} + \dfrac3{3!} + \dfrac4{4!} + \cdots

can be rewritten as 0 0 ! + 1 1 ! + 2 2 1 + 3 3 2 ! + 4 4 3 ! + \dfrac0{0!} + \dfrac1{1!} + \dfrac2{2*1} + \dfrac3{3*2!} + \dfrac4{4*3!} + \cdots

0 0 ! + 1 1 ! + 2 2 1 + 3 3 2 ! + 4 4 3 ! + \implies \dfrac0{0!} + \dfrac1{1!} + \dfrac{\color{#D61F06}{\cancel{\color{#333333}{2}}}}{\color{#D61F06}{\cancel{\color{#333333}{2}}}*1} + \dfrac{\color{#D61F06}{\cancel{\color{#333333}{3}}}}{{\color{#D61F06}{\cancel{\color{#333333}{3}}}}*2!} + \dfrac{\color{#D61F06}{\cancel{\color{#333333}{4}}}}{{\color{#D61F06}{\cancel{\color{#333333}{4}}}}*3!} + \cdots

0 0 ! + 1 0 ! + 1 1 ! + 1 2 ! + 1 3 ! + Note: 0! = 1, which also meant 0!=1! \implies \dfrac0{0!} + \dfrac1{0!} + \quad \dfrac1{1!} \quad + \quad \dfrac1{2!} \quad + \quad\dfrac1{3!}\quad + \cdots \qquad \qquad \color{#20A900}{\small\text{Note: 0! = 1, which also meant 0!=1!}}

Which is the same thing as e = 1 0 ! + 1 1 ! + 1 2 ! + 1 3 ! + e = \dfrac1{0!} + \dfrac1{1!} + \dfrac1{2!} + \dfrac1{3!} + \cdots

Therefore, the answer is True \color{#302B94}{\boxed{\Huge {\text{True}}}}

Correctttt!

Very neat and colorful solution too!

Pi Han Goh - 4 years, 9 months ago
Chew-Seong Cheong
Aug 25, 2016

e x = k = 0 x k k ! d d x e x = d d x k = 0 x k k ! e x = 0 + k = 1 k x k 1 k ! Putting x = 1 e = 0 0 ! + 1 1 ! + 2 2 ! + 3 3 ! + 4 4 ! + . . . \begin{aligned} e^x & = \sum_{k=0}^\infty \frac {x^k}{k!} \\ \frac d{dx} e^x & = \frac d{dx} \sum_{k=0}^\infty \frac {x^k}{k!} \\ e^x & = 0 + \sum_{k=1}^\infty \frac {kx^{k-1}}{k!} & \small \color{#3D99F6}{\text{Putting }x=1} \\ \implies \boxed{e} & = \frac 0{0!} + \frac 1{1!} + \frac 2{2!} + \frac 3{3!} + \frac 4{4!} + ... \end{aligned}

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