# CBSE Class 10-Mathematics: Questions and Answers Chapter – 10 Circles Part 20 (For CBSE, ICSE, IAS, NET, NRA 2022)

Get top class preparation for CBSE/Class-10 right from your home: get questions, notes, tests, video lectures and more- for all subjects of CBSE/Class-10.

Question 3:

Prove that opposite sides of a quadrilateral circumscribing a circle subtend supplementary angles at the center of the circle.

Given: ABCD is a quadrilateral circumscribing a circle whose center is O.

To prove: (i)

(ii)

Construction: Join OP, OQ, OR and OS.

Proof: Since tangents from an external point to a circle are equal.

In OBP and ,

[Common]

[From eq. (i) ]

[By SSS congruence criterion]

Similarly,

Since the sum of all the angles round a point is equal to .

Similarly, we can prove that

Question 4:

In the given figure XY and X ‘Y’ are two parallel tangents to a circle with center O and another tangent AB with point of contact C intersecting XY at A and X ‘Y’ at B. Prove that .

Join

In and , we have