Đáp án:

 a, `\hat{A}`=$60^o$, `\hat{B}`=$90^o$, `\hat{C}`=$30^o$

b, $\widehat{A}$=`60^o`, `\hat{B}`=$60^o$, $\widehat{C}$=$60^o$

c,$\widehat{C}$=`65^o`, `\hat{B}`=`45^o`

d, $\widehat{A}$=$30^o$, $\widehat{B}$=$60^o$, $\widehat{C}$=$90^o$

Giải thích các bước giải:

a, Trong $\triangle$ABC có: $\widehat{A}$+$\widehat{B}$+$\widehat{C}$=$180^o$

$\widehat{2C}$+$\widehat{3C}$+$\widehat{C}$=$180^o$

$\widehat{6C}$=$180^o$

$\widehat{C}$=$180^o$:6

$\widehat{C}$=$30^o$

Mà $\widehat{A}$=$\widehat{2C}$=2.$30^o$=$60^o$

$\widehat{B}$=$\widehat{3C}$=3.`30^o`=`90^o`

b, Trong $\triangle$ABC có: $\widehat{A}$+$\widehat{B}$+$\widehat{C}$=$180^o$

Vì: $\widehat{A}$=$\widehat{B}$=$\widehat{C}$ nên $\widehat{ABC}$= $180^o$:3=$60^o$