Question

determine o 20° termo e a soma ( s20) seguinte pa ( 2,7,12,17...)

Answer 1

a1 = 2
a2 = 7
r = 7 - 2 = 5 *****
n = 20
a20 = a1 + 19r
a20 = 2 + 19(5)
a20 = 2 + 95  = 97 *****
S20 = (a1 + a20)* n/2
S20 = ( 2 + 97)*10
S20 = 99 * 10 = 990 ****