Question

find the sum of the A.P a=70 tn=7 d=-3​

Answer 1

$given - -$

$first \: term \: = a = 70$

$no. \: of \: term = t _{n} = 7$

$commom \: diff. = d = - 3$

$s = \frac{n}{2} (2a + (n - 1) d))$

$s = \frac{7}{2} (2 \times 70 + (7 - 1) \times ( - 3))$

$s = \frac{7}{2} (140 - 18)$

$s = \frac{7}{2} \times (122)$

$s = 7 \times 61$

$s = 427$