Toán Lớp 6: Tính hoặc rút gọn :
2+4+6+…+100
2+2^3+2^5+….+2^99
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Toán Lớp 6: Tính hoặc rút gọn :
2+4+6+…+100
2+2^3+2^5+….+2^99
Comments ( 2 )
={(100+2)[(100-2):2+1]}/2
={102[98:2+1]}/2
={102[49+1]}/2
={102.50}/2
=[102.25.2]/2
=102.25
=2550
Đặt A=2+2^3+2^5+….+2^99
=>2^2A=2^3+2^5+2^7+….+2^101
=>4A-A=(2^3+2^5+2^7+….+2^101)-(2+2^3+2^5+….+2^99)
=>3A=2^101-2
=>A=[2^101-2]/3