Rút gọn :

\(-\dfrac{14}{35}=-\dfrac{2}{5}\)

\(-\dfrac{27}{63}=-\dfrac{3}{7}\)

\(-\dfrac{27}{65}=-\dfrac{27}{65}\)

\(-\dfrac{36}{84}=-\dfrac{3}{7}\)

a) Hai góc đối đỉnh khi tổng độ dài hai góc là 180^o.

Ta có tổng độ dài hai góc trên là : 70 + 70 = 140^o vậy hai góc trên không đối đỉnh.

b) Sửa hai góc có chung đỉnh thành khác đỉnh

a)\(\dfrac{3}{7}x-2\dfrac{1}{3}=0,5\)

\(\dfrac{3}{7}x=0,5+2\dfrac{1}{3}\)

\(\dfrac{3}{7}x=\dfrac{17}{6}\)

\(x=\dfrac{17}{6}:\dfrac{3}{7}\)

\(x=\dfrac{119}{18}\)

b)\(\dfrac{4}{7}-\dfrac{2}{3}:x=1\dfrac{1}{4}\)

\(\dfrac{2}{3}:x=\dfrac{4}{7}-1\dfrac{1}{4}\)

\(x=\dfrac{2}{3}:\left(-\dfrac{19}{28}\right)\)

\(x=-\dfrac{56}{57}\)

c)\(\left(\dfrac{2}{3}x+2\dfrac{1}{4}\right):3\dfrac{1}{5}=0,75\)

\(\dfrac{2}{3}x+2\dfrac{1}{4}=0,75:3\dfrac{1}{5}\)

\(\dfrac{2}{3}x=\dfrac{15}{64}-2\dfrac{1}{4}\)

\(x=-\dfrac{129}{64}:\dfrac{2}{3}\)

\(x=-\dfrac{387}{128}\)

\(\left(2x-1\right)\left(x+\dfrac{2}{3}\right)=0\)

Vậy \(x-1=\dfrac{2}{3}\)

\(x=\dfrac{2}{3}+1\)

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

\(\dfrac{3}{7}x-\dfrac{2}{3}x=\dfrac{10}{21}\)

\(x\left(\dfrac{3}{7}-\dfrac{2}{3}\right)=\dfrac{10}{21}\)

\(-\dfrac{5}{21}x=\dfrac{10}{21}\)

\(x=\dfrac{10}{21}:\left(-\dfrac{5}{21}\right)\)

\(x=-2\)

\(\left(\dfrac{-6}{11}\right)\times\dfrac{7}{10}\times\left(\dfrac{11}{-6}\right)\times\left(-20\right)\)

=\(\left(\dfrac{-6}{11}\right)\times\left(\dfrac{11}{-6}\right)\times\dfrac{7}{10}\times\left(-20\right)\)

=\(1\times\left(-14\right)\)

=\(-14\)

\(\left(-1\dfrac{1}{2}\right):\dfrac{3}{4}\times\left(-4\dfrac{1}{2}\right)\)

=\(\left(-1\dfrac{1}{2}\right)\times\left(-4\dfrac{1}{2}\right):\dfrac{3}{4}\)

=\(\dfrac{27}{4}:\dfrac{3}{4}\)

=\(9\)