Question

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Answer 1

Bagi 2 kasus:
(1 + 1/4 + 1/16 + ... ) + (1/9 + 1/25 + 1/49 + ...) = a
(1/ (1 - 1/4)) + (1/9 + 1/25 + 1/49 + ...) = a
4/3 + (1/9 + 1/25 + 1/49 + ...) = a
1/9 + 1/25 + 1/49 + ... = a - (4/3)

Answer 2

Biar keliatan ada unsur deret geo tak hingga apa nggak, kta perbanyak anggota deret di atas :
1 + 1/4 + 1/9 + 1/16 + 1/25 + 1/136 + 1/49 + 1/64 + ... = a
dipisah,
(1/4 + 1/16 + 1/36 + 1/64 + ... ) + (1/9 + 1/25 + 1/49 + ... ) = a - 1
1/4 (1 + 1/4 + 1/9  +1/16 + ... ) + (1/9 + 1/25 + 1/49 + ... ) = a - 1
1/4 a + (1/9 + 1/25 + 1/49 + ... ) = a - 1
1/9 + 1/25 + 1/49 + ... = a - 1 - 1/4 a = 3/4 a - 1