Rational numbers/Stupid rule/No positive solution/Exercise

Show that the "rule“

${}{\frac {a}{b}}+{\frac {c}{d}}={\frac {a+c}{b+d}}\,$

is for ${}a,c\in \mathbb {N} _{+}$ (and ${}b,d,b+d\in \mathbb {Z} \setminus \{0\}$) never true. Give an example with ${}a,b,c,d,b+d\neq 0$

where this rule holds.

Create a solution