Question

If a=5, d=-3, then S25 = ____​

Answer 1

Answer:

-775

Step-by-step explanation:

$Sn=n/2(2a+(n-1)d)\\\\S_{25} =25/2(2*5+(25-1)(-3))\\ = 25/2 (10+24(-3))\\ = 25/2 (10- 72)\\ = 25/2(-62)\\ =25(-31)\\ = -775$