●ɪꜰ ᴛᴡᴏ ᴄɪʀᴄʟᴇꜱ ɪɴᴛᴇʀꜱᴇᴄᴛ ᴀᴛ ᴛᴡᴏ ᴘᴏɪɴᴛꜱ,ᴘʀᴏᴠᴇ ᴛʜᴀᴛ ᴛʜᴇɪʀ ᴄᴇɴᴛʀᴇ ʟɪᴇ ᴏɴ ᴛʜᴇ ᴘᴇʀᴘᴇɴᴅɪᴄᴜʟᴀʀ ʙɪꜱᴇᴄᴛᴏʀ ᴏꜰ ᴛʜᴇ ᴄᴏᴍᴍᴏɴ ᴄʜᴏʀᴅ?¿
Answers
Tᴡᴏ ᴄɪʀᴄʟᴇ ᴡɪᴛʜ ᴄᴇɴᴛʀᴇ O ᴀɴᴅ O′ɪɴᴛᴇʀsᴇᴄᴛ ᴀᴛ A ᴀɴᴅ B. AB ɪs ᴄᴏᴍᴍᴏɴ ᴄʜᴏʀᴅ ᴏғ ᴛᴡᴏ ᴄɪʀᴄʟᴇ OO′ ɪs ᴛʜᴇ ʟɪɴᴇ ᴊᴏɪɴɪɴɢ ᴄᴇɴᴛʀᴇ
Lᴇᴛ OO′ ɪɴᴛᴇʀsᴇᴄᴛ AB ᴀᴛ P
Iɴ OAO ᴀɴᴅ OBO′ ᴡᴇ ʜᴀᴠᴇ
OO′→ ᴄᴏᴍᴍᴏɴ
OA=OB→(ʀᴀᴅɪɪ ᴏғ ᴛʜᴇ sᴀᴍᴇ ᴄɪʀᴄʟᴇ)
O′A=O′B→(ʀᴀᴅɪɪ ᴏғ ᴛʜᴇ sᴀᴍᴇ ᴄɪʀᴄʟᴇ)
⇒ △OAO′≅△OBO′ {SSSᴄᴏɴɢᴜᴇɴᴄᴇ}
∠AOO′=∠BOO′ (CPCT)
ɪ.ᴇ., ∠AOP=∠BOP
Iɴ △AOP ᴀɴᴅ BOP ᴡᴇ ʜᴀᴠᴇ OP=OP ᴄᴏᴍᴍᴏɴ
∠AOP=∠BOP (ᴘʀᴏᴠᴇᴅ ᴀʙᴏᴠᴇ)
OA=OB (Rᴀᴅɪɪ ᴏғ ᴛʜᴇ sᴇᴍɪᴄɪʀᴄʟᴇ)
△APD=△BPD (SSSᴄᴏɴɢᴜᴇɴᴄᴇ)
AP=CP (CPCT)
ᴀɴᴅ ∠APO=∠BPO (CPCT)
Bᴜᴛ ∠APO+∠BPO=180
∴ ∠APO=90ᴏ
∴ AP=BP ᴀɴᴅ ∠APO=∠BPO=90ᴏ
∴ OO′ ɪs ᴘᴇʀᴘᴇɴᴅɪᴄᴜʟᴀʀ ʙɪsᴇᴄᴛᴏʀ ᴏғ AB
Tᴡᴏ ᴄɪʀᴄʟᴇ ᴡɪᴛʜ ᴄᴇɴᴛʀᴇ O ᴀɴᴅ O′ɪɴᴛᴇʀsᴇᴄᴛ ᴀᴛ A ᴀɴᴅ B. AB ɪs ᴄᴏᴍᴍᴏɴ ᴄʜᴏʀᴅ ᴏғ ᴛᴡᴏ ᴄɪʀᴄʟᴇ OO′ ɪs ᴛʜᴇ ʟɪɴᴇ ᴊᴏɪɴɪɴɢ ᴄᴇɴᴛʀᴇ
Lᴇᴛ OO′ ɪɴᴛᴇʀsᴇᴄᴛ AB ᴀᴛ P
Iɴ OAO ᴀɴᴅ OBO′ ᴡᴇ ʜᴀᴠᴇ
OO′→ ᴄᴏᴍᴍᴏɴ
OA=OB→(ʀᴀᴅɪɪ ᴏғ ᴛʜᴇ sᴀᴍᴇ ᴄɪʀᴄʟᴇ)
O′A=O′B→(ʀᴀᴅɪɪ ᴏғ ᴛʜᴇ sᴀᴍᴇ ᴄɪʀᴄʟᴇ)
⇒ △OAO′≅△OBO′ {SSSᴄᴏɴɢᴜᴇɴᴄᴇ}
∠AOO′=∠BOO′ (CPCT)
ɪ.ᴇ., ∠AOP=∠BOP
Iɴ △AOP ᴀɴᴅ BOP ᴡᴇ ʜᴀᴠᴇ OP=OP ᴄᴏᴍᴍᴏɴ
∠AOP=∠BOP (ᴘʀᴏᴠᴇᴅ ᴀʙᴏᴠᴇ)
OA=OB (Rᴀᴅɪɪ ᴏғ ᴛʜᴇ sᴇᴍɪᴄɪʀᴄʟᴇ)
△APD=△BPD (SSSᴄᴏɴɢᴜᴇɴᴄᴇ)
AP=CP (CPCT)
ᴀɴᴅ ∠APO=∠BPO (CPCT)
Bᴜᴛ ∠APO+∠BPO=180
∴ ∠APO=90ᴏ
∴ AP=BP ᴀɴᴅ ∠APO=∠BPO=90ᴏ
∴ OO′ ɪs ᴘᴇʀᴘᴇɴᴅɪᴄᴜʟᴀʀ ʙɪsᴇᴄᴛᴏʀ ᴏғ AB