Giúp mk vs các bác ơi ????????????????????????????

Question

Giúp mk vs các bác ơi
????????????????????????????
giup-mk-vs-cac-bac-oi

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Vodka 4 years 2020-10-15T03:48:21+00:00 1 Answers 90 views 0

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  1. Euphemia
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    2020-10-15T03:49:25+00:00
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    `a,` `|x+5|+|3-x|=7`

    Áp dụng tính chất : `|a|+|b|≥|a+b|`

    `⇒|x+5|+|3-x|≥|x+5+3-x|=|8|=8`

    `⇒|x+5|+|3-x|≥8` `(`trái với đề bài`)`

    $⇒x∈\varnothing$

    `b,` `|x+1/2|+|x+1/3|+|x+1/4|+|x+1/5|=5x` `(1)`

    Vì `|x+1/2|;|x+1/3|;|x+1/4|;|x+1/5|≥0` `∀x`

    `⇒|x+1/2|+|x+1/3|+|x+1/4|+|x+1/5|≥0`

    `⇒5x≥0`

    `⇒x≥0`

    `⇒x+1/2;x+1/3;x+1/4;x+1/5≥0`

    `⇒|x+1/2|=x+1/2;|x+1/3|=x+1/3;|x+1/4|=x+1/4;|x+1/5|=x+1/5`

    Thay vào `(1)`

    `⇒x+1/2+x+1/3+x+1/4+x+1/5=5x`

    `⇒4x+77/60=5x`

    `⇒x=77/60`

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