Vì ΔABC có
$\hat{A}$ = $\hat{B}$ = $\hat{C}$ ⇒ ΔABC là tam giác đều
$\hat{A}$ + $\hat{B}$ + $\hat{C}$ = `180^0` mà $\hat{A}$ = $\hat{B}$ = $\hat{C}$ (gt)
⇒ `180^0` = $\hat{A}$ + $\hat{B}$ + $\hat{C}$ = `180/3` = `60^0`
⇒ $\hat{A}$ = $\hat{B}$ = $\hat{C}$ = `60^0`