Question

calcule a soma dos 25 termos do PA(19,14....)

Answer 1

an = a1 + (n-1) . r
an = 19 + (25-1) . -5
an = 19 + 24. -5
an = 19 + - 120
an = - 101

sn = (a1 + an) . n/ 2
s25 = ( 19 + -101) . 25 / 2
s25 = - 82 . 25 / 2
s25 = - 2050 / 2
s25 = - 1025