Toán giúp mk với a |x|+1/3|+1/3|+1/3|=0 b 2/6+2/12+2/20+…+2/x(x+1)=4/5 21/08/2021 By Lydia giúp mk với a |x|+1/3|+1/3|+1/3|=0 b 2/6+2/12+2/20+…+2/x(x+1)=4/5
Giải thích các bước giải: a) `|x|+1/3+1/3+1/3=0` `=>|x|+1=0` `=>|x|=-1` $\text{(loại vì }|x|\geq0)$ b) `2/6+2/12+2/20+…+2/(x(x+1))=4/5` `=>2(1/6+1/12+1/20+…+1/(x(x+1)))=2. 2/5` `=>1/6+1/12+1/20+…+1/(x(x+1))=2/5` `=>1/2.3+1/3.4+1/4.5+…+1/(x(x+1))=2/5` `=>1/2-1/3+1/3-1/4+1/4-1/5+…+1/x-1/(x+1)=2/5` `=>1/2-1/(x+1)=2/5` `=>1/(x+1)=1/2-2/5=1/10` `=>x+1=10` `=>x=9` Trả lời
Đáp án: Giải thích các bước giải: $a) |||x|+\frac{1}{3}|+\frac{1}{3}|+\frac{1}{3}|=0 \\ \Leftrightarrow ||x|+\frac{1}{3}|+\frac{1}{3}| = \frac{-1}{3}(vô lí)\\b) Pt \Leftrightarrow \frac{1}{2.3} + \frac{1}{3.4} + … + \frac{1}{x(x+1)} = \frac{2}{5}\\\Leftrightarrow \frac{1}{2} -\frac{1}{3}+ \frac{1}{3} – \frac{1}{4} + … + \frac{1}{x} – \frac{1}{x+1} = \frac{2}{5}\\\Leftrightarrow \frac{1}{2} – \frac{1}{x+1} = \frac{2}{5}\\\Leftrightarrow \frac{1}{x+1} = \frac{1}{10}\Leftrightarrow x + 1 = 10 \Leftrightarrow x = 9$ Trả lời
Giải thích các bước giải:
a) `|x|+1/3+1/3+1/3=0`
`=>|x|+1=0`
`=>|x|=-1` $\text{(loại vì }|x|\geq0)$
b) `2/6+2/12+2/20+…+2/(x(x+1))=4/5`
`=>2(1/6+1/12+1/20+…+1/(x(x+1)))=2. 2/5`
`=>1/6+1/12+1/20+…+1/(x(x+1))=2/5`
`=>1/2.3+1/3.4+1/4.5+…+1/(x(x+1))=2/5`
`=>1/2-1/3+1/3-1/4+1/4-1/5+…+1/x-1/(x+1)=2/5`
`=>1/2-1/(x+1)=2/5`
`=>1/(x+1)=1/2-2/5=1/10`
`=>x+1=10`
`=>x=9`
Đáp án:
Giải thích các bước giải:
$a) |||x|+\frac{1}{3}|+\frac{1}{3}|+\frac{1}{3}|=0 \\
\Leftrightarrow ||x|+\frac{1}{3}|+\frac{1}{3}| = \frac{-1}{3}(vô lí)
\\
b) Pt \Leftrightarrow \frac{1}{2.3} + \frac{1}{3.4} + … + \frac{1}{x(x+1)} = \frac{2}{5}\\
\Leftrightarrow \frac{1}{2} -\frac{1}{3}+ \frac{1}{3} – \frac{1}{4} + … + \frac{1}{x} – \frac{1}{x+1} = \frac{2}{5}\\
\Leftrightarrow \frac{1}{2} – \frac{1}{x+1} = \frac{2}{5}\\
\Leftrightarrow \frac{1}{x+1} = \frac{1}{10}
\Leftrightarrow x + 1 = 10 \Leftrightarrow x = 9
$