\(\frac{1}{1.2}+\frac{1}{2.3}+...+\frac{1}{x.\left(x+1\right)}=\frac{2005}{2010}\)
\(\Leftrightarrow1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{x}-\frac{1}{x+1}=\frac{401}{402}\)
\(\Leftrightarrow1-\frac{1}{x+1}=\frac{401}{402}\)
\(\Leftrightarrow\frac{1}{x+1}=1-\frac{401}{402}\)
\(\Leftrightarrow\frac{1}{x+1}=\frac{1}{402}\)
\(\Leftrightarrow x+1=402\Rightarrow x=401\)
a,tim x biet |x-2|+|3-2x|=2x+1
b,tim x,y thuoc Z biet xy+2x-y=5
c, tinh A=(1-1/15)(1-1/21)(1-1/28).....(1-1/210)
tim x thuoc Z biet x^3-x^2+x-1=0
Tim x thuoc z biet:
A)(x-3)(2y+1)=7
B) (2x+1)(3y-2)=-55
1) Tim a, b thuoc Q biet: a-b=2(a+b)=a:b
2) Tim x thuoc Q sao cho: (x-1)(x+3)<0
tim x thuoc z biet
a) (x-1)(x+2) < 0
b) (x+3)(x-5) > 0
tim cac so x,y,z thuoc Q biet rang (x+y):(5-z):(y+z):(y+9)=3:1:2:5
tim x thuoc z biet /x+1/ +/x-2/+/x+7/=5x-10
a, Tim x biet:/x-2/+/3-2x/=2x+1
b, Tim x,y thuoc Z biet:xy+2x-y=5
c, tim x,y,z, biet :2x=3y;4y=5zva 4x-3y+5z=7
tim x thuoc z biet /x+1/ +/x-2/+/x+7/=5x-10
