Exercise 1

The bisectors of angles A and B of a scalene triangle ABC meet at O. (i) What is the point O called? (ii) OR and OQ is drawn a perpendicular to AB and CA respectively. What is the relation between OR and OQ? (iii) What is the relation between ∠ACO and ∠BCO?

Solution: (i) The point O where the angle bisectors meet is called the incenter of the triangle. (ii) The perpendicular drawn from point O to AB and CA are equal. i.e., OR and OQ. (iii) ∠ACO = ∠BCO....

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(i) Conduct a triangle ABC with BC = 6.4 cm, CA = 5.8 cm and ∠ ABC = 60°. Draw its incircle. Measure and record the radius of the incircle. (ii) Construct a ∆ABC with BC = 6.5 cm, AB = 5.5 cm, AC = 5 cm. Construct the incircle of the triangle. Measure and record the radius of the incircle. (2014)

Solution: Steps to construct: Step 1: Draw a line segment BC = 6.4cm. Step 2: Construct an angle of 60o at point B. Step 3: With C as center and radius CA = 5.8cm, draw an arc cutting BD at A. Step...

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Using a ruler and compasses only: (i) Construe a triangle ABC with the following data: Base AB = 6 cm, AC = 5.2 cm and ∠CAB = 60°. (ii) In the same diagram, draw a circle which passes through the points A, B and C. and mark its centre O.

Solution: Steps to construct: Step 1: Draw a line segment AB = 6cm. Step 2: At point A, draw a ray making an angle of 60o. Step 3: With B as the center and radius 5.2cm, draw an arc which intersects...

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Use a ruler and compass only in this question. (i) Draw a circle, centre O and radius 4 cm. (ii) Mark a point P such that OP = 7 cm. Construct the two tangents to the circle from P. Measure and record the length of one of the tangents.

Solution: Steps to construct: Step 1: Draw a circle with center O and radius 4cm and mark that point as A. Step 2: Take a point P such that OP = 7cm. Step 3: Bisect OB at M. Step 4: With center M...

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