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To find the common difference d we note that the $\\var{n1}$th term is $\\var{t1}$ and the $\\var{n2}$th term is $\\var{t2}$ so we can find the common difference d by noting $\\var{t2}-\\var{t1}=(\\var{n2}-\\var{n1})\\times d$, hence common difference $= \\var{d}$

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It is then straightforward to find the first term $a_1$ by substituting the common difference back into either of our given terms. For example, we know $\\var{t1} = a_1 + (\\var{n1}-1)\\times \\var{d}$, hence $a_1 = \\var{a}$

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What is the first term and the common difference?

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First term$=$[[0]]

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Common difference$=$[[1]]

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In an arithmetic series, the $\\var{n1}$th term is $\\var{t1}$ and the $\\var{n2}$th term is $\\var{t2}$

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