arithmetic progression - The first term of an arithmetic series is a and the common difference is d. The 18th term of the series is 25 and the 21st term of the series is 32.5

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arithmetic progression Q-A1.NS.21 High-school syllabus questions

Anonymous

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Use this information to write down two equations for a and d.

Krishna (last edited 4 years ago) (Expert, Educator @Qalaxia)

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Step 1: Note down the given terms, and write their equivalent term of the arithmetic sequence.

EXAMPLE: 18th term = a + (n-1)d = a + (18 - 1)d

= a + 17d

21th term = a + 20d

Step 2: Equate the given terms with the equivalent terms of arithmetic sequence. This will form the equations.

EXAMPLE: 18th term of the series is 25

a + 17d = 25