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A = \(\dfrac{1}{2}\) + \(\dfrac{1}{4}\) + \(\dfrac{1}{8}\) + \(\dfrac{1}{16}\)+ \(\dfrac{1}{32}\)+\(\dfrac{1}{64}\)+\(\dfrac{1}{128}\)
A\(\times\) 2 = 1 + \(\dfrac{1}{2}\) + \(\dfrac{1}{4}\) + \(\dfrac{1}{8}\) + \(\dfrac{1}{16}\)+ \(\dfrac{1}{32}\)+ \(\dfrac{1}{64}\)
A \(\times\) 2 - A = 1 - \(\dfrac{1}{128}\)
A\(\times\)(2-1) = \(\dfrac{128-1}{128}\)
A = \(\dfrac{127}{128}\)
Gọi \(\dfrac{1}{2}+\dfrac{1}{4}+\dfrac{1}{8}+\dfrac{1}{16}+\dfrac{1}{32}+\dfrac{1}{64}+\dfrac{1}{128}\) là B
\(B=\dfrac{1}{2}+\dfrac{1}{4}+\dfrac{1}{8}+\dfrac{1}{16}+\dfrac{1}{32}+\dfrac{1}{64}+\dfrac{1}{128}\)
\(2\cdot B=1+\dfrac{1}{2}+\dfrac{1}{4}+\dfrac{1}{8}+\dfrac{1}{12}+\dfrac{1}{32}+\dfrac{1}{64}\)
\(2\cdot B-B=1+\dfrac{1}{2}+\dfrac{1}{4}+\dfrac{1}{8}+\dfrac{1}{12}+\dfrac{1}{32}+\dfrac{1}{64}-\left(\dfrac{1}{2}+\dfrac{1}{4}+\dfrac{1}{8}+\dfrac{1}{16}+\dfrac{1}{32}+\dfrac{1}{64}+\dfrac{1}{128}\right)\)
\(B=1+\left(\dfrac{1}{2}-\dfrac{1}{2}+\dfrac{1}{4}-\dfrac{1}{4}+.....+\dfrac{1}{64}-\dfrac{1}{64}\right)-\dfrac{1}{128}\)
\(B=1+0-\dfrac{1}{128}\)
\(B=1-\dfrac{1}{128}\)
\(B=\dfrac{128}{128}-\dfrac{1}{128}\)
\(B=\dfrac{127}{128}\)
1/1x2 + 1/2x3 + 1/3x4 + 1/4x5 + 1/5x6 + 1/6x7
=1/1-1/2+1/2-1/3+...-1/7
=1+(1/2-1/2+1/3-1/3+...+1/6-1/6)-1/7
=1 +0+0+...-1/7
=1-1/7
=6/7
1/2:0,5-1/4:0,2+1/8:0,125+75%
= 50%:50%-25%:20%+12,5%:12.%5+75%
=1-25%:20%+12,5%+12.%5+75%
=75,75%
2019 + 2019 : 0,5 + 2019 : 0,2 + 2019 : 0,125
= 2019 x 1 + 2019 x 2 + 2019 x 5 + 2019 x 8
= 2019 x ( 1 + 2 + 5 + 8 )
= 2019 x 16
= 32304
Trl :
2019 + 2019 : 0,5 + 2019 : 0,2 + 2019 : 0,125
= 2019 x 1 + 2019 x 2 + 2019 x 5 + 2019 x 8
= 2019 x ( 1 + 2 + 5 + 8 )
= 2019 x 16
= 32304
(1-1/2)x(1-1/3)x...x(1-1/n)
= (1/2)x(2/3)x(3/4)x...x(n-1/n)
= 1x2x3x...xn-1/2x3x4x...xn
= 1/n
Cần gì thêm nhắn tin cho mk nhé, tks =)))
=2
tk mk
= 2 bn nhé
tk mk