Register Now

222-9+11+12:2*14+14 = ? ( )

## 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

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

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
=> 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 }

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
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