diketahui u3=8 , dan u5+u9=56 tentukan a) suku pertama b) beda c) u14 d)S20

U3 = a+2b = 8 => a= -2b+8
U5+U9 = 56 => a+4b+a+8b = 56 => 2a+12b = 56

a = -2b+8
2a+12b = 56
2(-2b+8)+12b = 56
-4b+16+12b = 56
8b = 56-16
8b = 40
b = 5

a = -2b+8
a = -2(5)+8 = -10+8 = -2

a) a = U1 = -2
b) b = 5
c) U14 = a+13b = -2+13(5) = -2+65 = 63
d) S20 = 20/2 (2×-2 + 19×5)
S20 = 10 (-4+95)
S20 = 10 (91)
S20 = 910

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Jadikan jawaban ter-Brainly yaa:)