Question

(-4)+(-1)+2+5+....+53

Answer 1

b = 3
a = -4
Un = a + (n-1)b
53 = (-4) + (n-1)3
53 + 4 = 3n-3
57 + 3 = 3n
60 = 3n
n = 60 : 3
n = 20
semoga membantu :)

Answer 2

Un=bn-(b-a)
    =3n-(3-(-4)
    =3n -7
53 = 3n-7
3n = 53+7=60
  n=60/3=20

Sn=n/2(2a+(n-1)b)
S20=20/2(2 x - 4 + (20-1)3)
S20=10(-8+(19x3)
S20=10(-8+57)
S20=10(49)=490