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Worked solution

Find two specified arithmetic terms

Find the third and seventh terms of an arithmetic progression with first term a=2a=2 and common difference d=0.5d=0.5.

CJC · Sequences and Series · Self-Practice 2

Answer

u3=3u_3=3, u7=5u_7=5.

Compare your reasoning

Count additions after the first term

u3=2+(3−1)(0.5)=3,u7=2+(7−1)(0.5)=5.\begin{aligned}u_3&=2+(3-1)(0.5)=3,\\u_7&=2+(7-1)(0.5)=5.\end{aligned}

The source prints the two answers; the substitutions explain the n−1 offset.

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