Question 109

Find the value of expression.
$$8\left(1 + \frac{1}{2} + \frac{1}{4}.....\infty\right)$$

Solution

$$8\left(1 + \frac{1}{2} + \frac{1}{4}.....\infty\right)$$ is an infinite GP (the expression under the brackets) with the first term being 1, and the common ratio being $$\frac{\ 1}{2}$$or 0.5.

For infinite GP with common ratio less than 1, the sum is $$\ \frac{\ a}{(1-r)}$$

Applying the same in this, we get the sum as $$\ \frac{\ 1}{(1-0.5)}$$, which is 2.

Hence, the value of the entire expression is $$8\times2$$, which is 16.


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