Toán Lớp 6: Tính tổng:
S= 3+(-2) ² -(-2) ³ +(-2)⁴ – ………………..-(-2)⁹⁹ +(-2)¹⁰⁰
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Toán Lớp 6: Tính tổng:
S= 3+(-2) ² -(-2) ³ +(-2)⁴ – ………………..-(-2)⁹⁹ +(-2)¹⁰⁰
Comments ( 1 )
=>(-2)S=-2[3+(-2)²-(-2)³+(-2)⁴-….-(-2)^99 +(-2)^100]
=>(-2)S=(-6)+(-2)³-(-2)⁴+(-2)⁵-…-(-2)^100 +(-2)^101
=>(-2)S+S=[(-6)+(-2)³-(-2)⁴+(-2)⁵-…-(-2)^100 +(-2)^101]-[3+(-2)²-(-2)³+(-2)⁴-….-(-2)^99 +(-2)^100 ]
=>(-1)S=(-6)-3+2^101
=>-S=-9+2^101
=>S=-(-9+2^101)
=>S=9-2^101
Vậy S=9-2^101