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  1. Consider the series 21 + 17 + 13 + … + −99 as you answer the questions in parts (a) through (c) below. Homework Help ✎

    1. Write an expression for the nth term.

    2. How many terms are in the series? How can you tell?

    3. What is the sum of this series?

Use a system of equations or look at the difference between terms and the value of the first term.

Set the equation you found in part (a) equal to −99 and solve for n.

Use the rectangle method or Antonio's method.