From a point outside a circle, the two tangents drawn are:
AAlways parallel
BDifferent in length
CAlways perpendicular
DEqual in length
Answer & Solution
Correct answer: D. Equal in length
### Theorem: Tangents from an External Point
**Given:** A circle with center $O$ and a point $P$ lying outside the circle. Two tangents $PA$ and $PB$ are drawn from $P$ to the circle, touching it at points $A$ and $B$ respectively.
**To Prove:** $PA = PB$
**Construction:** Join $OA$, $OB$, and $OP$.
**Step-by-Step Proof:**
1. **Identify Right Angles:** We know that the radius is perpendicular to the tangent at the point of contact. Therefore:
$$\angle OAP = \angle OBP = 90^\circ$$
2. **Compare Triangles:** In $\triangle OAP$ and $\triangle OBP$:
- $OA = OB$ (Radii of the same circle)
- $OP = OP$ (Common hypotenuse)
- $\angle OAP = \angle OBP = 90^\circ$
3. **Apply Congruence:** By the RHS (Right-Angle Hypotenuse Side) congruence criterion:
$$\triangle OAP \cong \triangle OBP$$
4. **Conclusion:** Since the triangles are congruent, their corresponding parts are equal (CPCT):
$$PA = PB$$
Therefore, the lengths of the tangents drawn from an external point to a circle are **equal in length**.
Keep practising Triangles and Circles
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