Question 21: Prove that: (i) the parallelogram inscribed in a circle is a rectangle (ii) the rhombus, inscribed in a circle is a square.
Answer:
(i) Let be a parallelogram inscribed in the circle.
(opposite angles of a parallelogram are equal)
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Similarly,
Therefore is a rectangle
(ii) is a rhombus (given) i.e. all four sides are equal.
Similarly,
Therefore is a square
Question 22: In the following figure . Prove that is an isosceles trapezium.
Answer:
(given)
is a cyclic quadrialteral)
… … … … (i)
(corresponding angles)
Hence
… … … … (ii)
Hence because of (i) and (ii), is an isosceles trapezium.
Question 23: Two circles intersect at and . Through diameters and of the two circles are drawn. Show that the points and are collinear.
Answer:
(angle in a semi circle)
(angle in a semi circle)
Therefore
Therefore are collinear.
Question 24: is a quadrilateral inscribed in a circle. having . is the center of the circle. Show that: .
Answer:
(cyclic quadrilateral)
(sum of the angles in a triangle is 180)
Similarly
Therefore
Question 25: The figure given below shows the circle with center . Given and . (i) Find the relationship between . (ii) Find if is a parallelogram.
Answer:
(i) and (given)
(ii) If is a parallelogram
Therefore (opposite angles are equal)
(radius of the same circle)
Hence
Question 26: Two chords and intersect at inside the circle. Prove that the sum of the angles subtended by the arcs and at the center is equal to twice the .
Answer:
Similarly,
Adding the two
… … … … (i)
In
… … … … (ii)
Using (1) and (ii)
Question 27: In the given figure is a diameter of the circle. and . Find (i) (ii)
Answer:
(i) (angle in a semi circle)
(ii) Given
(alternate angles)
Question 28: In the given figure, and is the center of the circle. If , find the . Give reasons.
Answer:
and (angles in a semi circle)
Since
In
(cyclic quadrilateral)
(angles in the same segment)
Question 29: Two circles intersect at and . Through a straight line is drawn to meet the circles in and . Through , a straight line is drawn to meet the circles at and . Prove that is parallel to .
Answer:
and are cyclic quadrilateral
… … … … (i)
… … … … (ii)
… … … … (iii)
From (i) and (ii)
… … … … (iv)
From (iv) and (iii)
… … … … (v)
Therefore by (v)
Question 30: is a cyclic quadrilateral in which and on being produced, meet at such that . Prove that is parallel to .
Answer:
is a cyclic quadrilateral, and (given)
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