a)\(\dfrac{\dfrac{2}{5}+\dfrac{2}{7}-\dfrac{2}{9}-\dfrac{2}{11}}{\dfrac{4}{5}+\dfrac{4}{7}-\dfrac{4}{9}-\dfrac{4}{11}}=\dfrac{2\cdot\left(\dfrac{1}{5}+\dfrac{1}{7}-\dfrac{1}{9}-\dfrac{1}{11}\right)}{4\cdot\left(\dfrac{1}{5}+\dfrac{1}{7}-\dfrac{1}{9}-\dfrac{1}{11}\right)}=\dfrac{2}{4}=\dfrac{1}{2}\)
b) \(\dfrac{7.9+14.27+21.36}{21.27+42.81+63.108}=\dfrac{7.9.\left(1+2.3+3.4\right)}{7.9.\left(3.3+6.9+8.12\right)}=\dfrac{1+2.3+3.4}{3.3+6.9+8.12}=\dfrac{1+6+12}{9+54+108}=\dfrac{19}{171}=\dfrac{1}{9}\)
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