a) Bạn tự vẽ
b) Ta có:
+) $\widehat{x'Ot'}=\widehat{xOt}\left(đối-đỉnh\right)$
+) $\widehat{t'Oy'}=\widehat{tOy}\left(đối-đỉnh\right)$
Mà: Góc xOt = góc tOy
=> Góc x'Ot' = góc t'Oy'
c) Ta có: $\widehat{x'Om}+\widehat{yOm}+\widehat{tOy}+\widehat{xOt}=180^0$
Mà:
+) $\widehat{x'Om} = \widehat{yOm} (GT)
+) \widehat{tOy}=\widehat{xOt}$ (GT)
=> $2.\widehat{yOm}+2.\widehat{tOy}=180^0$
=> $2.\left(\widehat{yOm}+\widehat{tOy}\right)=180^0$
=> $\widehat{yOm}+\widehat{tOy}=180^0:2=90^0$
=> $\widehat{tOm}=90^0$