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a)
`9/2-3`
`=9/2-6/2`
`=3/2`
b)
`8/5xx25/12`
`=10/3`
c)
`4:3/7`
`=4xx7/3`
`=28/3`
a,x- 2/3= -1/2
x= -1/2 + 2/3
x= 1/6
b,20%.x - x +1/5 =3/4
1/5.x - x +1/5 = 3/4
1/5.x-x =3/4 - 1/5
x.(1/5 - 1)=11/20
x.-4/5 =11/20
x=11/20 : -4/5=-11/16
a) \(x-\frac{2}{3}=-\frac{1}{2}\)
\(\Leftrightarrow x=\frac{2}{3}-\frac{1}{2}\)
\(\Leftrightarrow x=\frac{1}{6}\)
b) \(20\%x-x+\frac{1}{5}=\frac{3}{4}\)
\(\Leftrightarrow\frac{1}{5}x-x=\frac{3}{4}-\frac{1}{5}\)
\(\Leftrightarrow-\frac{4}{5}x=\frac{11}{5}\)
\(\Leftrightarrow x=\frac{11}{5}:\left(-\frac{4}{5}\right)\)
\(\Leftrightarrow x=-\frac{11}{4}\)
\(\frac{1}{3.5}+\frac{1}{5.7}+\frac{1}{7.9}+...+\frac{1}{\left(2x+1\right).\left(2x+3\right)}=\frac{15}{93}\)
\(2.\left(\frac{1}{3.5}+\frac{1}{5.7}+\frac{1}{7.9}+...+\frac{1}{\left(2x+1\right).\left(2x+3\right)}\right)=2.\frac{15}{93}\)
\(\frac{2}{3.5}+\frac{2}{5.7}+\frac{2}{7.9}+...+\frac{2}{\left(2x+1\right).\left(2x+3\right)}=\frac{30}{93}\)
\(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{1}{2x+1}-\frac{1}{2x+3}=\frac{10}{31}\)
\(\frac{1}{3}-\frac{1}{2x+3}=\frac{10}{31}\)
\(\frac{1}{2x+3}=\frac{1}{3}-\frac{10}{31}\)
\(\frac{1}{2x+3}=\frac{1}{93}\)
=> 2x + 3 = 93
=> 2x = 93 - 3
=> 2x = 90
=> x = 90 : 2
=> x = 45
Vậy x = 45
=1/2x2/3x/3/4/.................x2003/2004
= 1x2x3x................x2003
___________________
2x3x4x................x 2004
=1/2004
tổng trên có số số hạng là:
(x-1):1+1=x (số)
tổng trên là:
(x+1)x:2=820
=> (x+1)x=820.2=1640=41.40
=>x=40
\(\frac{x^2-1}{x^2+1}=\frac{3}{4}\)
\(\Leftrightarrow4\left(x^2-1\right)=3\left(x^2+1\right)\)
\(4x^2-4=3x^2+3\)
\(x^2=7\)
\(x=\pm\sqrt{7}\)