Question

calcule a soma 10 primeiros Pa 12, 6,10

Answer 1

a1 = 12
n = 10
r = 6 - 12 ==> r = - 6

an = a1 + (n - 1) . r

a10 = 12 + (10-1) . (-6)

a10 = 12 + 9 .(-6)

a10 = 12 + (-54)

a10 = 12 - 54

a10 = - 42


Sn = (a1 + an) . n
........_________
................2

S10 = (a1 + a10) . n
..........__________
..................2

S10 = (12 + (-42)) . 10
..........____________
.......................2

S10 = ( 12 - 42) . 10
..........__________
...................2

S10 = - 30 x 10
............_______
....................2

S10 = - 300
............_____
.................2

S10 = - 150