Question

a soma doa 8 primeiro termo da pg (320,160,80

Answer 1

S8 = ?
a1 = 320
a2 = 160
q = 160/320 = 1/2 ***
a8 = a1q⁷
a8 = 320 * (1/2)⁷ = 320 * 1/128 = 320/128  = 5/2
S8 = [ a1 ( qⁿ   - 1 ) ]/ ( q - 1)
S8 = 320 [( 1/2)⁸ - 1 ] / ( 1/2 - 1/1)
S8 = 320[ 256  - 1 ] / ( - 1/2)
S8 = 320 [ 255] / ( - 1/2)
S8 = 81600/1 / ( - 1/2)
S8 = 81600/1 * (  - 2/1 ) = - 163200 *****