Finding the sum of arithmetic sequence when given two sums
By Emma Martinez •
How do you calculate this? The sum of $4$ terms of an arithmetic sequence is $42$ and the sum of the $3^{rd}$ and $7^{th}$ term is $46$. How do you find the sum of $20$ terms?
$Sn = n/2 [2a+d(n−1)]$ is the equation for working out the sum of an arithmetic series, but how can i rearrange to find for the first term and common difference. I belive it would be using simulatenous equations.
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