Correct Answer: AB ² + CD ² = BC ² + AD ²

Solution : According to the question,

Using Pythagoras theorem,
In $\triangle$ABC
AB ² = AC ² + BC ² ...........................................(i)
In $\triangle$ACD
AD ² = AC ² + CD ²
AC ² = AD ² – CD ² ...........................................(ii)
Put the value of AC ² in equation (i)
AB ² = AD ² – CD ² + BC ²
AB ² + CD ² = AD ² + BC ²
Hence, the correct answer is AB ² + CD ² = BC ² + AD ² .