Question

na pa (3,9,12,...,45) calcule a soma de todos os elementos

Answer 1

r = a2 -a1

r = 9 - 3

r = 6
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an = 45

an = ak + (n-k)*r

an = a1 + (n-1)*r

45 = 3 + (n-1)*6

45 = 3 + 6n -6

45 - 3 +6 = 6n

48 = 6n

n =  48/6

n = 8
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Sn = n(a1+an)/2

S8 = 8*(3 + 45)/2

S8 = 4( 48 )

S8 = 192