(1-1/3)X(1-1/6)X(1-1/10)x...x(1-1/190)
Tìm x biết : X x (1+1/3+1/6+1/10+1/15+...+1/190)=2013x19/10
X * ( 1 + 1/3 + 1/6 + 1/10 + 1/15 + ...... + 1/190 )
tìm x biết \(|x+1|+|x+\frac{1}{3}|+|x+\frac{1}{6}|+|x+\frac{1}{10}|+...+|x+\frac{1}{190}|=20x\) =20x
Ta có \(\left|x+1\right|\ge0;\left|x+\frac{1}{3}\right|\ge0;...;\)\(\left|x+\frac{1}{190}\right|\ge0\) \(\forall x\)
=> \(\left|x+1\right|+\left|x+\frac{1}{3}\right|+\left|x+\frac{1}{6}\right|+...+\left|x+\frac{1}{190}\right|\ge0\) \(\forall x\)
=> \(20x\ge0\Rightarrow x\ge0\)
Với \(x\ge0\) => \(x+1>0,x+\frac{1}{3}>0,x+\frac{1}{6}>0,...,x+\frac{1}{190}>0\)
=> \(\left|x+1\right|=x+1,\left|x+\frac{1}{3}\right|=x+\frac{1}{3},\left|x+\frac{1}{6}\right|=x+\frac{1}{6},...,\left|x+\frac{1}{190}\right|=x+\frac{1}{190}\)
=> \(x+1+x+\frac{1}{3}+x+\frac{1}{6}+...+x+\frac{1}{190}=20x\)
=> \(19x+\left(1+\frac{1}{3}+\frac{1}{6}+...+\frac{1}{190}\right)=20x\)
=> \(x=\left(1+\frac{1}{3}+\frac{1}{6}+...+\frac{1}{190}\right)\)
Gọi \(A=1+\frac{1}{3}+\frac{1}{6}+\frac{1}{10}+...+\frac{1}{190}\)
=> \(\frac{1}{2}A=\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+...+\frac{1}{380}\)
=> \(\frac{1}{2}A=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+...+\frac{1}{19.20}\)
=> \(\frac{1}{2}A=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{19}-\frac{1}{20}\)
=> \(\frac{1}{2}A=1-\frac{1}{20}\)
=> \(A=\frac{19}{10}\)
Thay vào ta có
=> \(x=-\frac{19}{10}\)
mk nhầm nha bạn \(x=\frac{19}{10}\)
bài 1 Rút gọn B=(1 -1/3).(1 -1/6).(1 -1/10).(1 -1/15)...(1 -1/190)
Bài 2 Tìm x biết
a) 1/21+ 1/28+ 1/36+..+1/x(x+1)=2/9
b)1/5.8 + 1/8.11+ 1/11.14+..+1/x(x+3)=101/1540
Cho A = \(\frac{1}{3}+\frac{1}{6}+\frac{1}{10}+\frac{1}{15}+...+\frac{1}{190}\)
Tính A x 10
Cho A = \(\frac{1}{3}+\frac{1}{6}+\frac{1}{10}+\frac{1}{15}+...+\frac{1}{190}\)
Tính A X 10
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7 [ x + 5 ] - 20 = 190 155 - 10 [ x + 1 ]= 55
6 [ x + 2 mũ 3 ] + 40 = 100 15x - 133 = 17
90 [ x + 2 ] = 45 14x + 54= 82
17x - 20 =14
A, 7[x + 5] - 20 = 190
7x + 35 - 20 = 190
7x + 15 = 190
7x = 175
x = 25
B, 155 - 10[x + 1] = 55
155 - 10x - 10 = 55
-10x + 90 = 55
-10x = -35
x = 3.5
C, 6[x + 2^3] + 40 = 100
6[x + 8] + 40 = 100
6x + 48 + 40 = 100
6x + 88 = 100
6x = 1
2 x = 2
D, 15x - 133 = 17
15x = 150
x = 10
E, 90[x + 2] = 45
90x + 180 = 45
90x = -135
x = -1.5
F, 4x + 54 = 82
4x = 28
x = 7
G, 17x - 20 = 14
17x = 34
x = 2
tìm x, biết :
a) 1/( x+1 ).( x+2 ) + 1/( x+2 ).( x+3 ) + 1/( x+3 ).( x+4 ) + ... + 1/( x+1999).( x+2000) = 1/x+200 = 1/5
b) 2/( x+1 ).( x+3 ) + 3/( x+3 ) .( x+6 ) + 4/( x+6 ).( x+10 ) + ... + 10/( x+45 ).( x+55 ) + 1/ x+55 = 1/6
A= ( 6 : 3/5 - 1 1/6 x 6/7 ) : ( 4 1/5 x 10/11 + 5 2/11 )
B= ( 1 - 1/2 ) x ( 1- 1/4 ) x ... x ( 1 - 1/2003 ) x ( 1 - 1/2004 )
C= 5 9/10 : 3/2 - ( 2 1/3 x 4 1/2 - 2 x 2 1/3 ) : 7/4
Giúp mình nhanh nha! Mình sẽ thick người đó