Toán Lớp 6: p= 7 – 7 mũ 3 + 7 mũ 5 – 7 mũ 7 +… -7 mũ 101
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Toán Lớp 6: p= 7 – 7 mũ 3 + 7 mũ 5 – 7 mũ 7 +… -7 mũ 101
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P = 7 – 7^3 + 7^5 – 7^7 + …. – 7^101
7^2 . P = 7^2 . ( 7 – 7^3 + 7^5 – 7^7 + …. – 7^101 )
49 . P = 7^3 – 7^5 + 7^7 – 7^9 + …. – 7^103
P + 49 . P = ( 7 – 7^3 + 7^5 – 7^7 + …. – 7^101 ) + ( 7^3 – 7^5 + 7^7 – 7^9 + …. – 7^103 )
50 . P = 7 – 7^103
P = ( 7 – 7^103 )/50
Vậy , P = ( 7 – 7^103 )/50
P = 7 – 7^3 + 7^5 – 7^7 + … – 7^101
=> 7^2P = 7^3 – 7^5 + 7^7 – 7^9 + … – 7^103
=> P + 49P = ( 7 – 7^3 + 7^5 – 7^7 + … – 7^101 ) + ( 7^3 – 7^5 + 7^7 – 7^9 + … – 7^103 )
=> 50P =7 – 7^103
=> P = {7 – 7^103}/50
Vậy P = {7 – 7^103}/50
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