D=1/2+1/14+1/35+.......+1/152
1/2+1/14+1/35+1/65+1/104+1/152 = ?
1/2+1/14+1/35+1/65+1/104+1/152= 12/19.
1/2+1/14+1/35+1/65+1/104+1/152
đây là bài tính nhanh , mong các bạn giúp đỡ
1/2+1/14+1/35+1/65+1/104+1/152
Tính tổng
D = 1/2 + 1/14 + 1/35 + ... + 1/434.
E = 2/15 + 3/40 + 11/152 + 13/608 + 25/1824 + 30/4959.
D = \(\frac{1}{2}+\frac{1}{14}+\frac{1}{35}+...+\frac{1}{434}\)
= \(2.\left(\frac{1}{4}+\frac{1}{28}+\frac{1}{70}+...+\frac{1}{868}\right)\)
= \(2.\frac{1}{3}.\left(\frac{3}{4}+\frac{3}{28}+\frac{3}{70}+...+\frac{3}{868}\right)\)
= \(\frac{2}{3}.\left(\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+...+\frac{3}{28.31}\right)\)
= \(\frac{2}{3}.\left(1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+...+\frac{1}{28}-\frac{1}{31}\right)\)
= \(\frac{2}{3}.\left(1-\frac{1}{31}\right)\)
= \(\frac{2}{3}.\frac{30}{31}\)
= \(\frac{20}{31}\)
E = \(\frac{2}{15}+\frac{3}{40}+\frac{11}{152}+\frac{13}{608}+\frac{25}{1824}+\frac{30}{4959}\)
= \(\frac{2}{3.5}+\frac{3}{5.8}+\frac{11}{8.19}+\frac{13}{19.32}+\frac{25}{32.57}+\frac{30}{57.87}\)
= \(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{8}+\frac{1}{8}-\frac{1}{11}+\frac{1}{11}-\frac{1}{19}+\frac{1}{19}-\frac{1}{32}+\frac{1}{32}-\frac{1}{57}+\frac{1}{57}-\frac{1}{87}\)
= \(\frac{1}{3}-\frac{1}{87}\)
= \(\frac{28}{87}\)
Tính:
a) C = 3/1.3 + 3/3.5 + 3/3.7 +...+ 3/49.51
b) D = 1/2 + 1/14 + 1/35 + 1/65 + 1/104 + 1/152
a; C = \(\dfrac{3}{1.3}\) + \(\dfrac{3}{3.5}\) + \(\dfrac{3}{3.7}\) + ... + \(\dfrac{3}{49.51}\)
C = \(\dfrac{3}{2}\).(\(\dfrac{2}{1.3}\) + \(\dfrac{2}{3.5}\) + \(\dfrac{2}{5.7}\) + ... + \(\dfrac{2}{49.51}\))
C = \(\dfrac{3}{2}\).(\(\dfrac{1}{1}\) - \(\dfrac{1}{3}\) + \(\dfrac{1}{3}\) - \(\dfrac{1}{5}\) + \(\dfrac{1}{5}\) - \(\dfrac{1}{7}\) + ... + \(\dfrac{1}{49}\) - \(\dfrac{1}{51}\))
C = \(\dfrac{3}{2}\).(\(\dfrac{1}{1}\) - \(\dfrac{1}{51}\))
C = \(\dfrac{3}{2}\).\(\dfrac{50}{51}\)
C = \(\dfrac{25}{17}\)
a=1/2+1/14+1/35+1/65+1/104+1/152
tìm S= 1/2 +1/14 + 1/35+ 1/ 65+ 1/104+ 1/152
Tính A=1/2+1/14+1/35+1/65+1/104+1/152
\(\frac{1}{2}+\frac{1}{14}+\frac{1}{35}+\frac{1}{65}+\frac{1}{104}+\frac{1}{152}=\frac{12}{19}\)
Ai đồng ý với ý kiến của mk thì , mk sẽ tích lại gấp đôi!!!!!!
1 Tính nhanh:
a. 1/15+1/35+1/63+1/99+1/143
b. 1/2+1/14+1/35+1/65+1/104+1/152
2 Chứng minh: D=(1/2)^2 +(1/3)^2 +(1/4)^2 +....+(1/10)^2 bé hơn 1