Question

afla nr a daca ab+ac=520 si b+c=52

Answer 1

ab+ac=520
a(b+c)=520
a·52=520
a=520/52
a=10

:)

Answer 2

$\left \{ {{ab+ac=520} \atop {b\\ +\\ c=52}} \right. \left \{ {{a(b+c)=520} \atop {b+c=52}} \right. \left \{ {{a*52=520} \atop {b+c=52}} \right. \left \{ {{a\\\\ =\\ 10} \atop {b+c=52}} \right.$