Tangent Secant Theorem (A Maths Tuition)

Nice Proof of Tangent Secant Theorem:

http://www.proofwiki.org/wiki/Tangent_Secant_Theorem

Note: The term “Square of Sum less Square” means a^2-b^2=(a+b)(a-b)

The proof of the Tangent Secant Theorem, though not tested, is very interesting. In particular, the proof of the first case (DA passes through center) should be accessible to stronger students.

The illustration for theorem about tangent and...
The illustration for theorem about tangent and secant (Photo credit: Wikipedia)