a: \(x=\dfrac{5}{21}:\dfrac{-3}{7}=\dfrac{-5}{21}\cdot\dfrac{7}{3}=\dfrac{-35}{63}=\dfrac{-5}{9}\)
b: =>x=5 hoặc x=-5
c: =>2x=-1/4+5/3=-3/12+20/12=17/12
=>x=17/24
d: =>1/3x+2/5x-2/5=0
=>11/15x=2/5
=>x=2/5:11/15=2/5*15/11=30/55=6/11
e: =>\(x=\left(0.5\right)^2\cdot\left(-0.5\right)^3=-\left(0.5\right)^5\)
f: \(x=\dfrac{0.49^3}{0.7^2}=\dfrac{0.7^6}{0.7^2}=0.7^4\)