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18. (-1)n+1 19. (-1)n Vn n= 1 (n + 1)2 n=1 n + 2 20. Approximate the sum of the series by using the first five terms. (-1)n 2 . Find the maximum amount of error for this approximation. n! n=1 21 . Approximate the sum of the convergent series (-1)n so that the error will be less than 0.001. ( 2n ) ! 72= 0 B. How many terms are needed? How do you know that your approximation is guaranteed to be within 0.001 of the exact value? Justify your