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U5+U7=36
S10=...?
U3 --> a+2b=9... (1)
U5+U7 --> (a+4b)+(a+6b)=36
2a+10b=36....(2)
dari pers 1 diperoleh
a+2b=9
a=9-2b ....(3)
masukkan pers 3 ke pers 2
2(9-2b)+10b=36
18-4b+10b=36
6b=18
b=3
masukkan b ke pers 3
a=9-2(b)
a=9-6
a=3
S10 = 10/2 (2a+(10-1)b)
=5 (2.3+(9).3)
=5 (6+27)
=5(33)=165