Question

cacule a soma dos 15 primeiros termos de P.A (-45,-41,-37,-33...)

Answer 1

P.A ( -45,-41,-37-33.....)
An=a1+(n-1)•r
A15=-45+(15-1)• 4
A15= -45+56
A15 = 11


S15 = 15 • ( -45 + 11)/2

S15 = 7,5 • (- 34 )
S15 = -255