Question

Tìm x: a) 2x - 5x = -1/21 ÷ -5/84 _________ b) 1/2x - 2/3x + 1/5 = -3/4

Answer 1

a: =>-3x=1/21*84/5=4/5

=>x=-4/5:3=-4/15

b: =>-1/6x=-3/4-1/5=-19/20

=>x=19/20:1/6=19/20*6=57/10

Answer 2

#\(N\)

`a,`\(2x-5x=-\dfrac{1}{21}\div-\dfrac{5}{84}\)

\(2x-5x=\dfrac{4}{5}\)

\(x.\left(2-5\right)=\dfrac{4}{5}\)

\(-3x=\dfrac{4}{5}\)

\(x=\dfrac{4}{5}\div-3\)

\(x=-\dfrac{4}{15}\)

`b,` \(\dfrac{1}{2}x-\dfrac{2}{3}x+\dfrac{1}{5}=-\dfrac{3}{4}\)

\(\dfrac{1}{2}x-\dfrac{2}{3}x=-\dfrac{3}{4}-\dfrac{1}{5}\)

\(\dfrac{1}{2}x-\dfrac{2}{3}x=-\dfrac{19}{20}\)

\(x.\left(\dfrac{1}{2}-\dfrac{2}{3}\right)=-\dfrac{19}{20}\)

\(x.-\dfrac{1}{6}=-\dfrac{19}{20}\)

\(x=-\dfrac{19}{20}\div-\dfrac{1}{6}\)

\(x=\dfrac{57}{10}\)