Fractal Fractions

Algebra Level 2

3 4 + 3 4 + 3 4 + 3 4 + 3 4 + 3 4 + 3 4 + . . . 4 4 4 4 4 4 4 = ? \large \frac { 3 }{ 4 } +\frac { \frac { 3 }{ 4 } +\frac { \frac { 3 }{ 4 } +\frac { \frac { 3 }{ 4 } +\frac { \frac { 3 }{ 4 } +\frac { \frac { 3 }{ 4 } +\frac { \frac { 3 }{ 4 } +\frac { ... }{ 4 } }{ 4 } }{ 4 } }{ 4 } }{ 4 } }{ 4 } }{ 4 } = \ ?

(This fraction goes on indefinitely)


The answer is 1.

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2 solutions

Julian Poon
Jun 25, 2014

let,

3 4 + 3 4 + 3 4 + 3 4 + . . . 4 4 4 4 = x \frac { 3 }{ 4 } +\frac { \frac { 3 }{ 4 } +\frac { \frac { 3 }{ 4 } +\frac { \frac { 3 }{ 4 } +\frac { ... }{ 4 } }{ 4 } }{ 4 } }{ 4 } =x

Since the fraction goes on for infinity,

x = 3 4 + x 4 = 3 + x 4 x=\frac { 3 }{ 4 } +\frac { x }{ 4 } =\frac { 3+x }{ 4 }

Solving it gives x = 1 x=1

Therefore, the answer is 1

Easier..i used same one

Yoogottam Khandelwal - 5 years, 11 months ago
Mark H
Jul 14, 2014

Consider a sequence of a n {a_n} , where:

a n = 3 + a n 1 4 a_n = \frac{3+a_{n-1}}{4}

lim n a n = L \lim_{n\to\infty} a_n = L because we can assume this fraction converges to a limit (otherwise we wouldn't be able to do this problem), we know that as n , a n = a n + 1 n\to\infty, a_n = a_{n+1}

So:

L = lim n a n + 1 L = \lim_{n\to\infty} a_{n+1}\\ apply the recursive definition: L = lim n 3 + a n 4 L = 3 + L 4 4 L = 3 + L 3 L = 3 L = 1 L = \lim_{n\to\infty} \frac{3+a_n}{4}\\ L = \frac{3+L}{4}\\ 4L = 3+L\\ 3L = 3\\ L = 1 lim n a n = 1 \lim_{n\to\infty} a_n = 1

Could you explain the meaning of lim? i want to learn these

Yoogottam Khandelwal - 5 years, 11 months ago

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Lim means limit .It is a sub-topic in calculus.

Bala vidyadharan - 5 years, 10 months ago

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