Tangent and Secant
- If a secant and a tangent of a circle are drawn from a point outside the circle, then the product of the lengths of the secant and its external segment equals the square of the length of the tangent segment

6² = 4(x + 4) ← substituted into theorem
36 = 4x + 16 ← distributive property
20 = 4x ← subtracted 16 from each side
x = 5 ← divided each side by 4