=> (1/1.2 + 1/2.3 + 1/3.4 + ... + 1/8.9 + 1/9.10) : x = 9/20
=> (1/1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + ... + 1/8 - 1/9 + 1/9 - 1/10) : x = 9/20
=> (1 - 1/10) : x = 9/20
=> 9/10 : x = 9/20
X = 9/10 : 9/20 = 2
Cho T=1/2+1/6+1/12+1/20+1/30+...+1/72+1/90.Tính T.
Cho T = 1/2 + 1/6 + 1/12 + 1/20 + 1/30 +....+1/72 + 1/90
\(\frac{9}{10}-\frac{1}{90}-\frac{1}{72}-\frac{1}{56}-\frac{1}{42}-\frac{1}{30}-\frac{1}{20}-\frac{1}{12}-\frac{1}{6}-\frac{1}{2}\)
Cho T = 1/2+1/6+1/12+1/20+1/30+.....+1/72+1/90. Tính T
tính bằng cách thuận tiện:1/2+ 1/6+ 1/12+ 1/20 +1/30+ 1/42+ 1/56 +1/72+ 1/90
tính nhanh:
1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90
\(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+\frac{1}{72}+\frac{1}{90}+\frac{1}{110}.\)
a) 3 \ x= y \ 40 = 12 \ 20
b) 6 \ x = 1 \ y = 18 \ 72
c) 9 \ x + 12 = 27 \ 69
Tính nhanh: A. 1/2 +1/4+1/8+1/16+1/32+1/64+1/128. B. 1/2 + 1/6 + 1/12 + 1/20 + 1/30 + 1/42 + 1/56 + 1/72 + 1/90 + 1/110 Các bạn giúp mình với mình cảm ơn
