Ta có 2 trường hợp:
TH1:
Ta có:
\(\widehat{SIR}=\widehat{OIR}-\widehat{SIO}\)
\(\Rightarrow\widehat{SIR}=90^o-60^o\)
\(\Rightarrow\widehat{SIR}=30^o\)
\(\Rightarrow\widehat{NIR}=\widehat{SIN}=\dfrac{\widehat{SIR}}{2}=\dfrac{30^o}{2}=15^o\)
Vậy...
TH2:
Ta có:
\(\widehat{SIR}=\widehat{SIO}+\widehat{OIR}\)
\(\Rightarrow\widehat{SIR}=60^o+90^o\)
\(\Rightarrow\widehat{SIR}=150^o\)
\(\Rightarrow\widehat{NIR}=\widehat{SIN}=\dfrac{\widehat{SIR}}{2}=\dfrac{150^o}{2}=75^o\)
Vậy...