Bài 2 : Tìm x nguyên biết : |x-1|+|x-2|+...|x-100|=605x
Bài 3 : Tìm x biết |x-1|+|x-2|+|y-3|+|x-4|=3
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|x + 1| + |x + 2| + |x + 3| + ...... + |x + 100| = 605x
Có : |x + 1| + |x + 2| + |x + 3| + ...... + |x + 100| \(\ge\)0
=> 605x \(\ge\) 0
=> x \(\ge\)0
<=> x + 1 + x + 2 + x + 3 + ...... + x + 100 = 605x
<=> 100x + 5050 = 605x
<=> 505x = 5050
<=> x = 10
|x + 1| + |x + 2| + |x + 3| + ...... + |x + 100| = 605x
Có : |x + 1| + |x + 2| + |x + 3| + ...... + |x + 100| \(\ge\)0
=> 605x \(\ge\) 0
=> x \(\ge\)0
<=> x + 1 + x + 2 + x + 3 + ...... + x + 100 = 605x
<=> 100x + 5050 = 605x
<=> 505x = 5050
<=> x = 10
Bài 2:
\(\dfrac{1}{x}+\dfrac{1}{x+2}+\dfrac{x-2}{x\left(x+2\right)}\)
\(=\dfrac{x+x+2+x-2}{x\left(x+2\right)}=\dfrac{3x}{x\left(x+2\right)}=\dfrac{3}{x+2}\)
Để 3/x+2 là số nguyên thì \(x+2\in\left\{1;-1;3;-3\right\}\)
hay \(x\in\left\{-1;-3;1;-5\right\}\)
`@` `\text {Ans}`
`\downarrow`
`2+(x+3)=7`
`\Rightarrow x+3=7-2`
`\Rightarrow x+3=5`
`\Rightarrow x=5-3`
`\Rightarrow x=2`
`5+(3+x)=10`
`\Rightarrow 3+x=10-5`
`\Rightarrow 3+x=5`
`\Rightarrow x=5-3`
`\Rightarrow x=2`
`(4+x)+1=7`
`\Rightarrow 4+x=7-1`
`\Rightarrow 4+x=6`
`\Rightarrow x=6-4`
`\Rightarrow x=2`
`(x+5)+3=9`
`\Rightarrow x+5=9-3`
`\Rightarrow x+5=6`
`\Rightarrow x=6-5`
`\Rightarrow x=1`
`(x-1)-4=7`
`\Rightarrow x-1=7+4`
`\Rightarrow x-1=11`
`\Rightarrow x=11+1`
`\Rightarrow x=12`
`4-(6-x)=1`
`\Rightarrow 6-x=4-1`
`\Rightarrow 6-x=3`
`\Rightarrow x=6-3`
`\Rightarrow x=3`
\(2+\left(x+3\right)=7\)
\(\Rightarrow2+x+3=7\)
\(\Rightarrow x+5=7\)
\(\Rightarrow x=2\)
\(5+\left(3+x\right)=10\)
\(\Rightarrow5+3+x=10\)
\(\Rightarrow x+8=10\)
\(\Rightarrow x=2\)
\(\left(4+x\right)+1=7\)
\(\Rightarrow4+x+1=7\)
\(\Rightarrow x+5=7\)
\(\Rightarrow x=2\)
\(\left(x+5\right)+3=9\)
\(=x+5+3=9\)
\(\Rightarrow x+8=9\)
\(\Rightarrow x=1\)
\(\left(x-1\right)-4=7\)
\(\Rightarrow x-1-4=7\)
\(\Rightarrow x-5=7\)
\(\Rightarrow x=12\)
\(4-\left(6-x\right)=1\)
\(\Rightarrow4-6-x=1\)
\(\Rightarrow-2-x=1\)
\(\Rightarrow x=-3\)