Question

The algebraic expression of an arithmetic sequence is 3-5n find its first term common difference and sum of first 20 terms

Answer 1

Answer:

$a = - 2 \\ \\ d = - 5 \\ \\ s = - 970.$

Step-by-step explanation:

$first \: term = a = 3 - 5(1) \\ = 3 - 5 \\ \\ = - 2. \\ \\ \\ \\ \\ \\ second \: term = 3 - 5(2) \\ \\ = 3 - 10 \\ \\ = - 7 \\ \\ \\ therefore \: \: \: \: \: \: \: \: d = common \: difference = - 7 + 2 \\ \\ = - 5$

$sum \: of \: first \: 20 \: terms = \frac{20}{2} ( - 2 + 19( - 5)) \\ \\ = 10( - 2 - 95) \\ \\ = 10 \times - 97 \\ \\ = - 970.$