Question

calcule a soma dos 24 primeiros termos de cada P.A a) (2/3,8/3,14/3...) b)(7,7,7...) c) (-1/2,-1/4,0...)

Answer 1

a
a1 = 2/3
a2 = 8/3
r = 8/3 - 2/3 = 6/3 = 2 ***
n = 24
a24 = 2/3 + 23 ( 2 ) = 2/3 + 46/1 = ( 2 + 138)/3 = 140/3 ***
S24 =  ( 2/3 + 140/3)* 12
S24 = 142/3 * 12/1 = 1704/ 3 = 568
b

a1 = 7
a2 = 7
r = 7 - 7 = 0
a24 = 7
S24 = ( 7 + 7 )*12
S24 = 14 * 12  = 168 ou   24 * 7  = 168
PA{ 7,7,7,7,7,7,.....................7 ]

c
a1 = -1/2
a2 = - 1/4
r = -1/4 - ( - 1/2) = - 1/4 + 1/2 = ( -1 + 2)/4 =1/4****
a24 = -1/2 + 23 (1/4)
a24 = -1/2 + 23/4 = ( -2 + 23)/4 = 21/4 ***
S24 = ( - 1/2 + 21/4)* 12
S24 = ( -2 + 21)/4   * 12/1 = 19/4 * 12/1 = 228/4 =57 ***