Question

Ka bantuannya Pakai caranya​

Answer 1

S3 = 21

n/2 (2a + (n-1)b) = 21

3/2 (2a + 2b) = 21

3a + 3b = 21 (setiap ruas dibagi 3)

a + b = 7

a = 7-b
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u1 x u3 = 40

a x (a+2b) = 40

a² + 2ab = 40

(7-b)² + 2b (7-b) = 40

49 -14b-b² + 14b -2b² = 40

49 - b² = 40

49-40 = b²

9 = b²

3 = b

a = 7-3 = 4
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deret aritmatika nya : 4,7,10

u1 x u2 = 4 x 7 = 28