Question

determine a soma dos vintes primeiros da pa 1,1/2,0..

Answer 1

P.A(1,1/2,0,........
A 1 = 1
A 2 = 1/2
R = A 2 - A 1
R = 1/2 - 1
R = -1/2
S 20 = 20.(A 1 + A 20 ) / 2
A 20 = A 1 + (N - 1 ).R
A 20  = 1 + (20 - 1 ).-1/2
A 20 = 1 + 19.-1/2
A 20 = 1  - 19/2
A 20 = -17/2
s20 = 20.(A 1 + A 20 )/2
S 20 = 20(1 + (-17/2)/2
S 20 = 20 . (1 - 17/2)/2
S 20 = 20 . (2 /2- 17/2 ) /2
S 20 = 20. (-15/2)/2
S 20 =-300/2  / 2
S 20 = -150/2
S 20 = -75