1.Tìm x, y thuộc Z :
50- 5*(x + 3 )3=2|3- y|
2.Tính :
a, \(\dfrac{-1}{20}+\dfrac{-1}{30}+\dfrac{-1}{42}+\dfrac{-1}{56}+\dfrac{-1}{72}+\dfrac{-1}{90}\)
b,\(\dfrac{5}{2.1}+\dfrac{4}{1.11}+\dfrac{3}{11.2}+\dfrac{1}{2.15}+\dfrac{13}{15.4}\)
3.Tìm x :
a, \(\dfrac{x-5}{8}=\dfrac{18}{x-5}\) b, ( x-2 )10= ( 2-x )8