Question

Даю 25 баллов!!!! Буду благодарен)))

Answer 1

а1=-8 d= 2. а20 = -8+ 2*19= 30. S20= (-8+30)*20/2= 440:2= 220

Answer 2

Sn=(А1+(n-1)*d/2)*n
a1=-8
d=2

S20=-8+(20-1)*2/2 *20=
=-8+19*2/2 *20=
=-8+38/2 *20=
=30/2 *20=
=15*20=300