Ta có: $\widehat{A1}$ `+` $\widehat{B}$ `+` $\widehat{x}$ `=` $180^{o}$
Hay $40^{o}$ `+` $60^{o}$ `+` $\widehat{x}$ `=` $180^{o}$
$100^{o}$ `+` $\widehat{x}$ `=` $180^{o}$
$\widehat{x}$ `=` $180^{o}$ `-` $100^{o}$
$\widehat{x}$ `=` $80^{o}$
Vì $\widehat{x}$ và $\widehat{n}$ là `2` góc kề bù
`→` $\widehat{x}$ `+` $\widehat{n}$ `=` $180^{o}$
Hay $80^{o}$ `+` $\widehat{n}$ `=` $180^{o}$
$\widehat{n}$ `=` $180^{o}$ `-` $80^{o}$
$\widehat{n}$ `=` $100^{o}$
Lại có: $\widehat{A2}$ `+` $\widehat{n}$ `+` $\widehat{m}$ `=` $180^{o}$
Hay $40^{o}$ `+` $100^{o}$ `+` $\widehat{m}$ `=` $180^{o}$
$140^{o}$ `+` $\widehat{m}$ `=` $180^{o}$
$\widehat{m}$ `=` $180^{o}$ `-` $140^{o}$
$\widehat{m}$ `=` $40^{o}$
Vậy $\widehat{n}$ `=` $100^{o}$
$\widehat{m}$ `=` $40^{o}$
