Question

determine a soma dos trinta primeiros termos:a)
p.a (3,6,9)
b)p.a(-5,-6,-7)
c) p.a(50,60,70)

Answer 1

a) 

an= a1+ ( n-1) . r
an= 3 + ( 30 -1) . 3
an= 3+ 29 . 3
an= 3+87
an= 90


b)

an=a1+(n-1) . r
an= -5 + ( 30 - 1) . 1
an= -5 + 29
an= 24


c)

an= a1 + ( n-1) . r
an= 50 + ( 30 -1 ) . 10
an= 50+29 . 10
an= 50 + 290
an= 340