# Proof without Words: $$\sum ar^n = a/(1-r)$$

by J. H. Webb

Mathematics Magazine
June, 1987

Subject classification(s): Sequences and Series | Geometric Sequence
Applicable Course(s): 2.1 College Algebra | 2.3 College Algebra & Trigonometry combined | 3.1 Mainstream Calculus I

The author presents a geometric proof for the sum of a geometric series by using similar triangles.

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