Question

calcule a soma dos 24primeiros termos da pa a)-57,-27,3.. b)2/3;8/3;14/3... c)7,7,7.." d)-1/2;-1/4;0...

Answer 1

a
a1 = -57
a2 = -27
a3 = 3
r =-27 - ( -57) = -27 + 57 = 30
n = 25
a24 = -7 + 23 ( 30)
a24 = 16 ( 30 ) = 480
S24 = ( -57 + 480)* 12
S24 = 423 * 12 =5076 ****

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