Toán Lớp 7: `x/20` = `5/x` `1/3`+x.`2/9`=`7/9`

Question

Toán Lớp 7:  x/20 = 5/x 1/3+x.2/9=7/9

baoquyen · Answer

$a)  frac{x}{20}= frac{5}{x}$   $xx=20.5$   $x^2=100$   $x=10, :x=-10$   $b)  frac{1}{3}+x frac{2}{9}= frac{7}{9}$   $ frac{1}{3}+x frac{2}{9}- frac{1}{3}= frac{7}{9}- frac{1}{3}$   $x frac{2}{9}= frac{4}{9}$   $9x frac{2}{9}= frac{4.9}{9}$   $2x=4$   $ frac{2x}{2}= frac{4}{2}$   $x=2$

kimnguenoanh · Answer

Lời giải và giải thích chi tiết:   x/20 = 5/x    text{&rArr; x&sup2; = 5 . 20}    text{&rArr; x&sup2; = 100}   &rArr;  ( left[  begin{array}{l}x=10&sup2;  x&sup2;=( - 10)&sup2; end{array}  right. ) &rArr;  ( left[  begin{array}{l}x=10  x=-10 end{array}  right. )    1/3 + x . 2/9 = 7/9               x . 2/9 = 7/9 - 1/3               x . 2/9 =  4/9                       x   =  4/9 : 2/9                       x    = 4/9 . 9/2                       x    =   2