A = 1/15 + 1/35 + 1/63 + 1/99 + ... + 1/129x15
giúp mình với đang cần gấp
Mình đang cần gấp lắm
M=1/3+1/6+1/12+1/24+1/48+1/96+1/192
N=7/3+7/15+7/35+7/63+7/99+7/143+7/195
Ai làm nhanh mk tik cho nha
N=7/2(2/1.3+....+2/13.15)
N=7/2.(1/1-1/3+.....+1/13-1/15)
N=7/2.(1-1/15)
N=7/2.(14/15)
N=7.14/2.15
Câu 1 .Tính nhanh :
a ) 7/19 × 8/23 + 7/19 × 15/23 + 1và7/19
b) 75/100 + 18/21 + 49/32 + 1/4 + 3/21 - 17/32
c)8/9 × 15/16 × 24/25 × 35/36 × 48/49 × 63/64
Hộ mình với ạ , mình đang cần gấp. Bạn nào làm đúng mình tick cho
\(\dfrac{7}{19}x\dfrac{8}{23}+\dfrac{7}{19}x\dfrac{15}{23}+1\dfrac{7}{19}\)
= \(\dfrac{7}{19}x\left(\dfrac{8}{23}+\dfrac{15}{23}\right)+1+\dfrac{7}{19}\)
=\(\dfrac{7}{19}x1+1+\dfrac{7}{19}\)
= \(\dfrac{7}{19}+1+\dfrac{7}{19}=1\dfrac{14}{19}\) = \(\dfrac{33}{19}\)
\(\dfrac{75}{100}+\dfrac{18}{21}+\dfrac{49}{32}+\dfrac{1}{4}+\dfrac{3}{21}-\dfrac{17}{32}\)
= \(\dfrac{3}{4}+\dfrac{6}{7}+\dfrac{49}{32}+\dfrac{1}{4}+\dfrac{1}{7}-\dfrac{17}{32}\)
= \(\left(\dfrac{3}{4}+\dfrac{1}{4}\right)+\left(\dfrac{6}{7}+\dfrac{1}{7}\right)+\left(\dfrac{49}{32}-\dfrac{17}{32}\right)\)
= 1 + 1 + 1 = 3
\(\dfrac{8}{9}x\dfrac{15}{16}x\dfrac{24}{25}x\dfrac{35}{36}x\dfrac{48}{49}x\dfrac{63}{64}\)
= \(\dfrac{3}{4}\) *Câu này bạn tự sử dụng gạch nhé!
`1,`
`a,`
`7/19 \times 8/23 + 7/19 \times 15/23 + 1 7/19`
`= 7/19 \times 8/23 + 7/19 \times 15/23 + 1 + 7/19`
`= 7/19 \times (8/23 + 15/23 + 1) + 1`
`= 7/19 \times 2 + 1`
`=14/19 + 1`
`= 33/19`
`b,`
`75/100 + 18/21 + 49/32 + 1/4 + 3/21 - 17/32`
`= 75/100 + (18/21 + 3/21) + (49/32 - 17/32) + 1/4`
`= 0,75 + 1 + 1 + 0,25`
`= (0,75 + 0,25) + 1 + 1`
`= 1+1+1=3`
`c,`
`8/9 \times 15/16 \times 24/25 \times 35/36 \times 48/49 \times 63/64`
`=` \(\dfrac{2\times3}{3\times3}\times\dfrac{3\times5}{4\times4}\times\dfrac{3\times4\times2}{5\times5}\times\dfrac{5\times7}{6\times6}\times\dfrac{6\times8}{7\times7}\times\dfrac{7\times9}{8\times8}\)
`= 3/4` (bạn sử dụng gạch, rút gọn các số là được nhé).
\(B=\frac{1}{3}+\frac{1}{15}+\frac{1}{35}+\frac{1}{63}+\frac{1}{99}=?\) ?
Cần gấp !!!
\(2B=\frac{2}{1.3}+\frac{2}{3.5}+....+\frac{2}{9.11}\)
\(2B=\frac{1}{1}-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+...+\frac{1}{9}-\frac{1}{11}\)
\(2B=\frac{1}{1}-\frac{1}{11}=\frac{10}{11}\)
\(B=\frac{10}{11}:2=\frac{10}{11}.\frac{1}{2}=\frac{5}{11}\)
\(B=\frac{1}{2}\left(\frac{2}{1.3}+\frac{2}{3.5}+...+\frac{2}{7.9}+\frac{2}{9.11}\right)\)
\(=\frac{1}{2}\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+...+\frac{1}{9}-\frac{1}{11}\right)\)
\(=\frac{1}{2}.\frac{10}{11}=\frac{5}{11}\)
B = 1/3 + 1/15 + 1/35 + 1/63 + 1/99
B = 1/2 × (2/1×3 + 2/3×5 + 2/5×7 + 2/7×9 + 2/9×11)
B = 1/2 × (1 - 1/3 + 1/3 - 1/5 + 1/5 - 1/7 + 1/7 - 1/9 + 1/9 - 1/11)
B = 1/2 × (1 - 1/11)
B = 1/2 × 10/11
B = 5/11
1. tính nhanh
1/3+1/15+1/25+1/35+1/63+1/99+1/143
giúp mình với
\(\dfrac{1}{3}+\dfrac{1}{15}+\dfrac{1}{25}+\dfrac{1}{35}+\dfrac{1}{63}+\dfrac{1}{99}+\dfrac{1}{143}\)
\(=\left(\dfrac{2}{1\cdot3}+\dfrac{2}{3\cdot5}+\dfrac{2}{5\cdot7}+\dfrac{2}{7\cdot9}+\dfrac{2}{9\cdot11}+\dfrac{2}{11\cdot13}\right)\cdot\dfrac{1}{2}+\dfrac{1}{25}\)
\(=\left(1-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+\dfrac{1}{7}-...+\dfrac{1}{11}-\dfrac{1}{13}\right)\cdot\dfrac{1}{2}+\dfrac{1}{25}\)
\(=\left(1-\dfrac{1}{3}\right)\cdot\dfrac{1}{2}+\dfrac{1}{25}\)
\(=\dfrac{2}{3}\cdot\dfrac{1}{2}+\dfrac{1}{25}\)
\(=\dfrac{1}{3}+\dfrac{1}{25}\)
\(=\dfrac{28}{75}\)
Tính:P=1/3+1/15+1/35+1/63+1/99 Help gấp
P=1/3+1/15+1/35+1/63+1/99
=1:3+1:15+1:35+1:63+1:99
=1:(3+15+35+63+99)
=1:215
=1/215
Vậy:P=1/215
Bài 2 : Tính
a) A= (1- 1/42) x (1-1/52) x (1-1/62) x ... x (1-1/2002)
b) B= 3/35 x 15/63 x 35/99 x ... x 9999/10815
Mình đag cần gấp
a) CÓ: A = (1-1/42).(1-1/52).(1-1/62)......(1-1/2002)
=\(\frac{4^2-1^2}{4^2}\). \(\frac{5^2-1^2}{5^2}\). \(\frac{6^2-1^2}{6^2}\)....... \(\frac{200^2-1^2}{200^2}\)
Ta có công thức sau : a2-b2= a2 -ab+ab-b2
= a(a-b) + b(a-b)
= (a+b)(a-b)
ÁP DỤNG CÔNG THỨC TRÊN VÀO BÀI TOÁN TA ĐƯỢC :
A= \(\frac{3.5}{4^2}\). \(\frac{4.6}{5^2}\). \(\frac{5.7}{6^2}\)......\(\frac{199.201}{200^2}\)
= \(\frac{\left(3.4.5.....199\right)\left(5.6.7....201\right)}{\left(4.5.6......200\right)^2}\)
= \(\frac{\left(3.4.5.......199\right)\left(5.6.7.....200.201\right)}{\left(4.5.6.....199.200\right)\left(4.5.6......200\right)}\)
= \(\frac{3.201}{200.4}\)
= \(\frac{603}{800}\)
b)Từ đề bài ta suy ra : B=\(\frac{1.3}{5.7}\).\(\frac{3.5}{7.9}\). \(\frac{5.7}{9.11}\)...... \(\frac{99.101}{103.105}\)
= \(\frac{1.3^2.5^2.7^2......99^2.101}{5.7^2.9^2.11^2....99^2.101^2.103^2.105}\)
=\(\frac{3^2.5}{101.103^2.105}\)
=\(\frac{3}{7500563}\)
Tính A= 1/15+ 1/35 + 1/63 +1/99 +...+ 1/9999
Bạn nào biết cách giải giải giùm mình cụ thể với .
\(A=\frac{1}{15}+\frac{1}{35}+\frac{1}{63}+\frac{1}{99}+...+\frac{1}{9999}\)
\(=\frac{1}{3.5}+\frac{1}{5.7}+\frac{1}{7.9}+\frac{1}{9.11}+...+\frac{1}{99.101}\)
\(=\frac{1}{2}.\left(\frac{1}{3}-\frac{1}{5}\right)+\frac{1}{2}.\left(\frac{1}{5}-\frac{1}{7}\right)+\frac{1}{2}.\left(\frac{1}{7}-\frac{1}{9}\right)+...+\frac{1}{2}\left(\frac{1}{99}-\frac{1}{101}\right)\)
\(=\frac{1}{2}.\left(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{1}{99}-\frac{1}{101}\right)\)
\(=\frac{1}{2}.\left(\frac{1}{3}-\frac{1}{101}\right)\)
\(=\frac{1}{2}.\frac{98}{303}\)
\(=\frac{49}{303}\)
Dấu chấm(.) ở cấp hai là dấu nhân (x)
A=1/15+1/35+1/63+1/99+1/143
ai tick mình
mình tk lại nhé
A=1/3.5+1/5.7+1/7.9+1/9.11+1/11.13
A=1/2 [1/3-1/5+1/5-1/7+1/7-1/9+1/9-1/11+1/11-1/13]
A=1/2.10/39
A=5/39
ai tk mình
mình tk lại
a,1/6+1/12+1/20+1/132
b,1/15+1/35+1/63+1/99+1/143
Giúp mình với sáng mai kiểm tra rồi
\(a)\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{132}\)
\(=\frac{22}{132}+\frac{11}{132}+\frac{1}{20}+\frac{1}{132}\)
\(=\frac{33}{132}+\frac{1}{20}+\frac{1}{132}\)
\(=\frac{34}{132}+\frac{1}{20}\)
\(=\frac{17}{66}+\frac{1}{20}\)
\(=\frac{203}{660}\)
\(a,\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{132}\)
\(=\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{132}\)
\(=\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}\right)+\frac{1}{132}\)
\(=\left(\frac{1}{2}-\frac{1}{5}\right)+\frac{1}{132}\)
\(=\frac{3}{10}+\frac{1}{132}\)
\(=\frac{198}{660}+\frac{5}{660}\)
\(=\frac{203}{660}\)
1/6 + 1/12 + 1/20 + ... + 1/132
= 1/2x3 + 1/3x4 + 1/3x4 + 1/4x5 + ... + 1/11x12
= 1/2 - 1/3 + 1/3 - 1/4 + 1/4 - 1/5 + .... + 1/11 + 1/12
= 1/2 - 1/12
= 5/12
Bài 2
= 1/3x5 + 1/5x7 + 1/7x9 + 1/9x11 + 1/11x13
= 1/2 x ( 2/3x5 + 2/5x7 + 2/7x9 + 2/9x11 + 2/11x13
= 1/2 x ( 2/3 - 2/5 + 2/5 - 2/7 + 2/7 - 2/9 + 2/9 - 2/11 + 2/11 - 2/13
= 1/2 x ( 2/3 - 2/13 )
= 1/2 x 20/39
= 10 / 39