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jawab

5ⁿ - 1  habis dibagi 4 -->  misal  5ⁿ - 1 = 4m (m, 1,2,3,...)

n = 1 --> 5 -1 = 4(1)

n= k --> 5^k  - 1 = 4|m

n= k+1 --> 5^(k+1) - 1 =
= 5. 5^k  - 1
= 4(5^k) - (5^k)   - 1
= 4. 5^k  - (5^k + 1)
= 4.5^k  - (4m)
= 4  (5^k - m)
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