## Exam-Style Question on Sigma## A mathematics exam-style question with a worked solution that can be revealed gradually |

Question id: 498. This question is similar to one that appeared on an IB Standard paper in 2009. The use of a calculator is allowed.

(a) Expand the following as the sum of six terms:

$$ \sum_{r=3}^{8} 2^r$$(b) Find the value of:

$$ \sum_{r=3}^{25} 2^r$$(c) Explain why the following cannot be evaluated:

$$ \sum_{r=3}^{\infty} 2^r$$
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