Toán Lớp 7: câu 2 a 2/3-(3/4+x)-1/3 b 2/5+3/5x- căn bậc 25/9 làm nhanh giùm mình với

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1. a) 2/3-(3/4+x)=1/3

   <=>3/4-x=2/3-1/3

   <=>3/4-x=1/3

   <=>x=1/3-3/4

   <=>x=-5/12

   Vậy x=-5/12

   b)2/5+3/5x=$\sqrt{\dfrac{25}{9} }$

   <=>2/5+3/5x=±5/3

   <=> \(\left[ \begin{array}{l} \dfrac{2}{5} + \dfrac{3}{5}x=\dfrac{5}{3} \\\dfrac{2}{5} + \dfrac{3}{5}x=-\dfrac{5}{3}\end{array} \right.\) 

   <=> \(\left[ \begin{array}{l} \dfrac{3}{5}x=\dfrac{5}{3}- \dfrac{2}{5} \\\ \dfrac{3}{5}x=-\dfrac{5}{3}-\dfrac{2}{5} \end{array} \right.\) 

   <=> \(\left[ \begin{array}{l} \dfrac{3}{5}x=\dfrac{19}{5} \\\ \dfrac{3}{5}x=-\dfrac{31}{15} \end{array} \right.\) 

   <=> \(\left[ \begin{array}{l} x=\dfrac{19}{5}:\dfrac{3}{5} \\\ x=-\dfrac{31}{15}: \dfrac{3}{5}\end{array} \right.\) 

   <=> \(\left[ \begin{array}{l} x=\dfrac{19}{19} \\\ x=-\dfrac{31}{9}\end{array} \right.\)

   Vậy x ∈{19/9;- 31/9}

   @thew

    

   Trả lời
2. a,

   2/3 – ( 3/4 + x ) = 1/3

   3/4 + x = 2/3 – 1/3

   3/4 + x = 1/3

   x = 1/3 – 3/4

   x = -5/12

   => x = -5/12

   b,

   2/5 + 3/5x =  $\sqrt{\dfrac{25}{9}}$

   2/5 + 3/5x = ±5/3

   – TH1: 2/5 + 3/5x = 5/3

   3/5x = 5/3 – 2/5

   3/5x = 19/15

   x = 19/15 : 3/5

   x = 19/9

   – TH2: 2/5 + 3/5x = -5/3

   3/5x = -5/3 – 2/5

   3/5x = -31/15

   x = -31/15 : 3/5

   x = -31/9

   => x ∈ { 19/9; -31/9 }

   Trả lời