Bài 21
a, \(33-14-26-\left(-7\right)\)
\(=33+7-14-26\)
\(=40-14-26\)
\(=26-26=0\)

b, \(\left(-5\right)-25-\left(-34\right)-4\)
\(=\left(-5\right)+\left(-25\right)+34-4\)
\(=-30+30=0\)

c,\(\left(-6\right)+5+\left(-4\right)+25 \)
\(=\left(-6\right)+\left(-4\right)+\left(5+25\right)\)
\(=-10+30=20\)

d, \(33+34+35+36-13-14-15-16\)
\(=\left(33-13\right)+\left(34-14\right)+\left(35-15\right)+\left(36-16\right)\)
\(=20+20+20+20=80\)

a, \(\dfrac{5}{7}+\left(\dfrac{3}{5}+\dfrac{-5}{7}\right)\)
\(=\dfrac{5}{7}+\dfrac{-5}{7}+\dfrac{3}{5} =0+\dfrac{3}{5}=\dfrac{3}{5}\)

b, \(=\dfrac{-3}{4}-\dfrac{15}{14}:\dfrac{-5}{7}+\left(-1\right)^2=\dfrac{-3}{4}-\dfrac{-3}{2}+1=\dfrac{-3}{4}-\dfrac{-6}{4}+1=\dfrac{3}{4}+1=\dfrac{7}{4}\)

 c, \(\dfrac{-5}{9}+\left(\dfrac{-2}{3}\right)^2.\left(20\%-1.2\right)=\dfrac{-5}{9}+\dfrac{4}{9}x\left(\dfrac{1}{5}-\dfrac{6}{5}\right)=\dfrac{-5}{9}+\dfrac{4}{9}x\left(-1\right)=\dfrac{-5}{9}+\dfrac{-4}{9}=-1\)