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Question
calculate the sum of 1 -2 +3 -4 +5 -6 +7 -8........+19 -20
Questioner: kevin
Country: United Arab Emirates
Category: Advanced Math
Question: calculate the sum of 1 -2 +3 -4 +5 -6 +7 -8........+19 -20
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This is called a 'telescoping sum', or something like that. Let's parenthesize it:
(1 - 2) + (3 - 4) + (5 - 6) + (7 - 8) + ........ + (19 - 20)
Each grouping adds to -1, and there are ten of them.
Does that do it for you?
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Paul Klarreich
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I can answer questions in basic to advanced algebra (theory of equations, complex numbers), precalculus (functions, graphs, exponential, logarithmic, and trigonometric functions and identities), basic probability, and finite mathematics, including mathematical induction. I can also try (but not guarantee) to answer questions on Abstract Algebra -- groups, rings, etc. and Analysis -- sequences, limits, continuity. I won't understand specialized engineering or business jargon.
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I taught at a two-year college for 25 years, including all subjects from algebra to third-semester calculus.
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