Find the value of
\(x = 1 + \cfrac{1}{2 + \cfrac{1}{2 + \cfrac{1}{2 + \cfrac{1}{2 + \ddots}}}}.\)
Here's how this is determined :
Evaluating from the "bottom" to the "top" .... we have....
2 + 1/2 = 5/2
2 + 2/5 = 12/5
2 + 5/12 = 29/12
2 + 12/29 = 70/29
1 + 29/70 = 1.4142857142857143 ...further expansion would get us closer and closer to the √2
Another way:
First: add 1 to both sides: x + 1 = 2 + [ 1 / [ 2 + [ 1 / [ 2 + 1 / [ ... ]
Let y = x + 1, then: y = 2 + [ 1 / [ 2 + [ 1 / [ 2 + 1 / [ ... ]
But [ 2 + [ 1 / [ 2 + 1 / [ ... ] = y
So: y = 2 + 1 / y
Multiply by y: y2 = 2y + 1
Set equal to 0: y2 - 2y - 1 = 0
Solve (using the quadratic formula): y = 1 +/- sqrt(2)
So: x + 1 = 1 +/- sqrt(2)
The negative answer can't be correct, so: x + 1 = 1 + sqrt(2) ---> x = sqrt(2)