Addition ou soustraction d'expressions fractionnaires de même dénominateur
\(\begin{array}{cc} \dfrac {a}{b} + \dfrac {a'}{b}= \dfrac {a+a'}{b}, & \dfrac {a}{b} - \dfrac {a'}{b}= \dfrac {a-a'}{b}.\end{array}\)
\(\begin{array}{cc} \dfrac {a}{b} + \dfrac {a'}{b}= \dfrac {a+a'}{b}, & \dfrac {a}{b} - \dfrac {a'}{b}= \dfrac {a-a'}{b}.\end{array}\)