Toán Lớp 6: tính tổng .2^12+2^14+2^16+…+2^140
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Toán Lớp 6: tính tổng .2^12+2^14+2^16+…+2^140
Giúp mik
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Đặt A=2^12 +2^14 +2^16 +…+2^140
=>2^2 A=2^2 (2^12 +2^14 +2^16 +…+2^140)
=>4A=2^14 +2^16 +2^18 +…+2^142
=>4A-A=(2^14 +2^16 +2^18 +…+2^142)-(2^12 +2^14 +2^16 +…+2^140)
=>3A=2^142 -2^12
=>A=(2^142 -2^12)/3
Vậy A=(2^142-2^12)/3