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Verified answer
Un = bn + a - bU3 = 3b + a - b
13 = 2b + a
Un = bn + a - b
U16 = 16b + a - b
78 = 15b + a
13 = 2b + a
78 = 15b + a
-------------------- -
-65 = -13b
b = -65/-13
b = 5
13 = 2b + a
13 = 2(5) + a
13 = 10 + a
a = 13 - 10
a = 3
Suku pertama (a) = 3
Beda (b) = 5