Question

given a=7 ,a13=35, find d and s13​

Answer 1

Answer:

your answer is given above.

Answer 2

Answer:

$t(n) = a + (n - 1)d \\ t(13) = 7 + 12d \\ 7 + 12d = 35 \\ 12d = 28 \\ d = \frac{7}{3}$

$s(13) = \frac{n}{2}(2a + (n - 1)d) \\ = > \frac{13}{2}(14 + 12 \times \frac{7}{3}) \\ = > \frac{13}{2}(14 + 28) \\ = > \frac{13}{2}(42) \\ = > s(13) = 273$

Step-by-step explanation:

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