The sum of the angles of a triangle is 180º Given: A triangle △ PQR and ∠1, ∠2, and ∠3 are angles of triangle △ PQR. To prove: ∠1 + ∠2 + ∠3 = 1800 Construction: Draw a line XPY parallel to QR passing through P. Proof: XPY ∥ QR and PQ is transversal ∴ ∠2 = ∠4 (Alternate angles) ….(1) XPY ∥ QR and PR […]
Read More →Converse of Pythagorean Theorem In this section we are going to see the converse of Pythagorean theorem. We know the Pythagorean theorem applies to right triangles and states that, The square of the length of the hypotenuse, equals the sum of the squares of the lengths of the other two sides. (hypotenuse)2 = (Base)2+(Perpendicular)2 […]
Read More →Theorem – The line segment joining the mid-points of two sides of a triangle is parallel to the third side. Given: A triangle △ABC, in which D and E are mid points of sides AB and AC respectively. DE is joined. To prove: Line joining the mid points D and E (DE) is parallel to the third line […]
Read More →Theorem : In a parallelogram, opposite angles are equal. Given: A parallelogram ABCD, opposite sides of parallelogram are side AB and side DC side AD and side BC. To prove: Opposite angles of parallelogram are equal. […]
Read More →Theorem – Alternate Interior Angles are Equal If a transversal intersects two parallel lines, then each pair of alternate interior angles are equal. Given: Two parallel Lines AB and CD, and PS be transversal intersecting AB at Q and CD at R. To Prove: Each pair of alternate interior angles are equal. i.e. ∠BQR = ∠CRQ and ∠AQR = ∠QRD […]
Read More →Theorem The perpendicular from the center of a circle to a chord bisects the chord. Given: A circle with center O, AB is chord of a circle and OC perpendicular from the center to the chord AB. i.e. OC ⊥ AB therefore ∠OCA and ∠OCB Both angles are 900. To prove: AC = CB (C is the mid point of chord AB) […]
Read More →The tangent at any point of a circle is perpendicular to the radius through the point of contact. Given: A circle with center O, and a tangent XY to the circle at a point P. Prove: OP ⟂ XY Proof : Let Q be any point on XY other than P and join OQ. The […]
Read More →The perpendicular from the center of a circle to a chord bisects the chord. Given: A circle with center O, AB is chord of a circle and OC perpendicular from the center O to the chord AB. i.e. OC ⊥ AB therefore ∠OCA and ∠OCB, Both angles are 900. To prove: AC = CB Construction: join OA and OB. Proof: In △OCA and △ OCB ∠OCA = ∠OCB […]
Read More →If a transversal intersects two lines, such that a pair of alternate interior angles are equal then the two lines are parallel. Given: Two lines AB and CD, and PS be transversal intersecting, AB at Q and CD at R. Each pair of alternate interior angles are equal. i.e. ∠BQR = ∠CRQ and ∠AQR = ∠QRD To Prove: AB ∥ CD Proof: Transversal […]
Read More →If the angles subtended by chords of a circle at the center are equal, then the chords are equal. Given: A circle with center O, AB and CD are chords of circle that subtend equal angles at center O. i,e. ∠AOB = ∠COD. To prove: chord AB = chord CD Proof: In △AOB and △ CODOA = OC (Radius of circle)∠AOB […]
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