cho tam giác ABC=DHK A=30 B=2C  Tính các góc còn lại của mỗi tam giác. 

`+)` Xét `Δ ABC`, ta có:

$\widehat{A}$ `+` $\widehat{B}$ `+` $\widehat{C}$ `= 180^o` ( Tổng `3` góc trong `1` tam giác)

Mà $\widehat{A}$`= 30^o` `;` $\widehat{B}$ `= 2`$\widehat{C}$

`=>` `30^o + 2`$\widehat{C}$`+` $\widehat{C}$ `= 180^o`

`=>``3`$\widehat{C}$`=180^o - 30^o`

`=>``3`$\widehat{C}$`=150^o`

`=>`$\widehat{C}$`=150^o : 3 = 50^o`

`+)` Ta có:

$\widehat{B}$ `=``2`$\widehat{C}$

`=>` $\widehat{B}$ `=``2. 50^o`

`=>` $\widehat{B}$ `=``100^o`

`+)` Vì `ΔABC = ΔDHK` (gt)

`=>` $\widehat{A}$ `=`  $\widehat{D}$`=30^o`

        $\widehat{B}$ `=`  $\widehat{H}$`=100^o`

        $\widehat{C}$ `=`  $\widehat{K}$ `= 50^o` 

                  (các góc tương ứng)

Xét $\triangle$ `ABC` có `:`

$\widehat{A}$ `+` $\widehat{B}$ `+` $\widehat{C}$ `=180^o`

Mà $\widehat{A}$ `=30^o` `;` $\widehat{B}$ `=` `2`$\widehat{C}$

`=>` `30^o` `+` `2`$\widehat{C}$ `+` $\widehat{C}$ `=180^o`

`=>` `3`$\widehat{C}$ `=150^o`

`=>` $\widehat{C}$ `=50^o`

Ta có `:`

$\widehat{B}$ `=` `2`$\widehat{C}$ `(g``t)`

`=>` $\widehat{B}$ `=2 . 50^o`

`=>` $\widehat{B}$ `=100^o`

Vì `:` `\triangle` `ABC` `=\triangle` `DHK` `(g``t)`

`=>` $\begin{cases} \widehat{A} = \widehat{D} =30^o\\\widehat{B} = \widehat{H} =100^o\\\widehat{C} = \widehat{K} =50^o \end{cases}$