TÍNH NHANH:1+1x2+2+2x3+6x8+5x5+9x2-3-8-1-1-3-4+6-8+5-7+6+56x10+23x10+135x100+234x100+1005x1000+10000x10000=?
A=5/9+2/15-6/9
B=2/7-3/8+4/7+1/7-5/8+5/15
C=3/5+1/15+1/57+1/3-2/9-3/4-1/36
D=1/1x2+1/2x3+1/3x4+...+1/99x100
E=1-3/1x3-3/3x5-3/5x7-...-19
help plssssssss
Giải:
A=5/9+2/15-6/9
=(5/9-6/9)+2/15
= -1/9 + 2/15
= 1/45
B=2/7-3/8+4/7+1/7-5/8+5/15
= (2/7+4/7+1/7) + (-3/8-5/8) +1/3
= 1+ (-1) +1/3
=1/3
C=3/5+1/15+1/57+1/3-2/9-3/4-1/36
=9/15+1/15+1/57+19/57-8/36-27/36-1/36
=(9/15+1/15)+(1/57+19/57)+(-8/36-27/36-1/36)
=2/3+20/57+(-1)
=58/57+(-1)
=1/57
D=1/1.2+1/2.3+1/3.4+...+1/99.100
=1/1-1/2+1/2-1/3+1/3-1/4+...+1/99-1/100
=1/1-1/100
=99/100
Câu E mình ko biết làm nhé!
Tính tổng sau bằng một cách hợp lí
A=5/7 cộng 8/11 cộng [-2/7] cộng 1/2 cộng 3/11
B=11/17 cộng [-8/19] cộng [-3/4] cộng 6/17 -30/19
C= 1/1x2 cộng 1/2x3 cộng 1/3x4 cộng .......... cộng 1/49x50
a: \(A=\dfrac{5}{7}-\dfrac{2}{7}+\dfrac{8}{11}+\dfrac{3}{11}+\dfrac{1}{2}=\dfrac{3}{7}+\dfrac{1}{2}+1=\dfrac{6+7+14}{14}=\dfrac{27}{14}\)
b: \(B=\dfrac{11}{17}+\dfrac{6}{17}-\dfrac{8}{19}-\dfrac{30}{19}+\dfrac{-3}{4}=1-2-\dfrac{3}{4}=-1-\dfrac{3}{4}=-\dfrac{7}{4}\)
c: \(C=1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+...+\dfrac{1}{49}-\dfrac{1}{50}=\dfrac{49}{50}\)
Bài 3 tính nhanh a,5/6-1/2-1/4-1/8-1/16 b,1/3+1/6+1/12+1/24+1/48+1/96 c,1/1x2+1/2x3+1/3x4+1/4x5+1/5x6 d,1/2+1/6+1/121/20+1/30+1/42 khẩn cấp aaaaa..... huhuhu.....
1. Tính
a) 5/7 x 4 : 5/9
b) 8 x 2/3 : 1/2
c) 6 : 3/5 - 7/6 x 6/7
21/5 x 10/11 + 57/11
2. Tìm x
a) 35/9 : x = 35/6
b) (1/1x2 + 1/2x3 + 1/3x4 +1/4x5 +1/5x6) x 10- x = 0
1> a) \(\frac{5}{7}x4:\frac{5}{9}=\frac{5}{7}:\frac{5}{9}x4=\frac{5}{7}x\frac{9}{5}x4=\frac{9}{7}x4=\frac{9x4}{7}=\frac{36}{7}\)
\(b,8x\frac{2}{3}:\frac{1}{2}=8x\frac{2}{3}x\frac{2}{1}=8x2x\frac{2}{3}=16x\frac{2}{3}=\frac{32}{3}\)
\(c,6:\frac{3}{5}-\frac{7}{6}x\frac{6}{7}=6x\frac{5}{3}-1=10-1=9\)
\(\frac{21}{5}x\frac{10}{11}+\frac{57}{11}=\frac{42}{11}+\frac{57}{11}=\frac{99}{11}=9\)
2) a) \(\frac{35}{9}:x=\frac{35}{6}\)
\(x=\frac{35}{9}:\frac{35}{6}\)
\(x=\frac{35}{9}x\frac{6}{35}\)
\(x=\frac{2}{3}\)
b) \(\left(\frac{1}{1x2}+\frac{1}{2x3}+\frac{1}{3x4}+\frac{1}{4x5}+\frac{1}{5x6}\right)x10-X=0\)
\(\left(\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+.....+\frac{1}{5}-\frac{1}{6}\right)x10-X=0\)
\(\left(\frac{1}{1}-\frac{1}{6}\right)x10-X=10\)
\(\frac{5}{6}x10-X=0\)
\(X=\frac{5}{6}x10=\frac{25}{3}\)
Đúng nha !!!!
1/a/\(\frac{5}{7}\cdot4:\frac{5}{9}=\frac{20}{7}:\frac{5}{9}=\frac{20}{7}\cdot\frac{9}{5}=\frac{36}{7}\)
b/\(8\cdot\frac{2}{3}:\frac{1}{2}=\frac{16}{3}:\frac{1}{2}=\frac{16}{3}\cdot\frac{2}{1}=\frac{32}{3}\)
c/\(6:\frac{3}{5}-\frac{7}{6}\cdot\frac{6}{7}=6\cdot\frac{5}{3}-1=10-1=9\)
2/a/\(\frac{35}{9}:x=\frac{35}{6}\)
\(x=\frac{35}{9}:\frac{35}{6}=\frac{35}{9}\cdot\frac{6}{35}\)
\(x=\frac{2}{3}\)
b/\(\left(\frac{1}{1\cdot2}+\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+\frac{1}{4\cdot5}+\frac{1}{5\cdot6}\right)\cdot10-x=0\)
\(\left(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}\right)\cdot10-x=0\)
\(\left(\frac{30}{60}+\frac{10}{60}+\frac{5}{60}+\frac{2}{30}\right)\cdot10-x=0\)
\(\frac{47}{60}\cdot10-x=0\)
\(\frac{47}{6}-x=0\)
\(x=\frac{47}{6}-0\)
\(x=\frac{47}{6}\)
Tìm X:
a,2xX-5=21
b,3/4+1/4xX=5/6
c,7/8-1/2xX=5/6
d(1/1x2+1/2x3+1/3x4)x100-[5/2:(X+206/100)]:1/2=89
\(a)\) \(2x-5=21\)
\(\Leftrightarrow\) \(2x=21+5\)
\(\Leftrightarrow\) \(2x=26\)
\(\Leftrightarrow\) \(x=26:2\)
\(\Leftrightarrow\) \(=13\)
\(b)\) \(\frac{3}{4}+\frac{1}{4}x=\frac{5}{6}\)
\(\Leftrightarrow\) \(\frac{1}{4}x=\frac{5}{6}-\frac{3}{4}\)
\(\Leftrightarrow\) \(\frac{1}{4}x=\frac{1}{12}\)
\(\Leftrightarrow\) \(x=\frac{1}{3}\)
\(c)\) \(\frac{7}{8}-\frac{1}{2}x=\frac{5}{6}\)
\(\Leftrightarrow\) \(\frac{1}{2}x=\frac{7}{8}-\frac{5}{6}\)
\(\Leftrightarrow\) \(\frac{1}{2}x=\frac{1}{24}\)
\(\Leftrightarrow\) \(x=\frac{1}{12}\)
tính nhanh
a)100-98+96-94+...+4-2
b)1+2-3-4+5+6-7+-8+9+10-11-12+13+2010
c)(864x11-423x4):(432x(3+6+9+...+27-132))
d)1x2+2x3+3x4+...+99x100
e)\(\frac{1+\left(1+2\right)+\left(1+2+3\right)+\left(1+2+3+4\right)+...+\left(1+2+3+...+99\right)}{1x9+2x98+3x97\: +....+99x1}\)
giúp mk với , mk tick cho 3 tick , nha !!!!
a,100-98+96-94+...+4-2
day tren so so so hang la (100-2):2+1=50
Có tất cả số cặp 5:2=25 cap
100-98+96-94+...+4-2=2+2+..+2=2.25=50
1+2+3+4+5+6+7+8+9x2:5= ??????????
1+2+3+4+5+6+7+8+9x2:5 = 1+2+3+4+5+6+7+8+18:5=1+2+3+4+5+6+7+8+3.6=39.6
1+2+3+4+5+6+7+8+9X2
1+2+3+4+5+6+7+8+9x2=1+2+3+4+5+6+7+8+18=54
Tính nhanh
A) (1 + 1/4) x (1+ 1/5) x(1+ 1/6) x....x (1+ 1/99)
B) 7/ 1x2 + 7/ 2x3 + 7/ 3x4 + ...... + 7/ 13x14
C) A = 1+ 1/3 +1/9 +1/27 + 1/81 +1/243