**FIRST TERM**

**SUBJECT: BASIC TECHNOLOGY**

**CLASS: JSS 2**

**REFERENCE MATERIALS**

- MELROSE, Basic Science and Technology, Book 2
- NERDC, Basic Technology for JSS, Book 2

**WEEK TEN**

**TOPIC: CONSTRUCTION OF TANGENT TO A CIRCLE**

**CONTENT**

- Construction Of Tangent To A Given Circle.

**HOW TO CONSTRUCT A TANGENT TO A CIRCLE AT A GIVEN POINT ON THE CIRCUMFERENCE**

**Procedure**

- Draw the given circle with centre O
- Indicate the given point P.
- Draw a line from centre O to pass through point P to extend outside the circle.
- With centre P and radius OP, draw an arc to cut the extended line at A.
- Bisect line OA.
- Join the bisecting points with a line BC
- BC is the required tangent

**HOW TO CONSTRUCT A TANGENT TO A CIRCLE FROM A GIVEN POINT OUTSIDE THE CIRCLE **

**Procedure **

- Draw the given circle with centre O.
- Indicate the point P to centre O
- Join point P to the centre O.
- Construct a semicircle on OP to cut the circle at A.
- A is point of tangency on the circle.
- Draw a line to join P to A to give the required.

**HOW TO CONSTRUCT A CIRCLE OF A GIVEN RADIUS TO TOUCH A GIVEN STRAIGHT LINE AND CIRCLE **

**Procedure **

- Draw the given straight line AB, and a circle O
- Draw a line parallel to line AB at a distance equal to the radius of the required circle.
- Take this length (radius of required circle R2 + radius of given circle R1.
- With O as centre, draw an arc to cut the parallel line at C.
- With centre C and radius CD, draw required circles.

**HOW TO CONSTRUCT A CIRCLE TO TOUCH THREE GIVEN LINES**

**Procedures**

- Draw the three given lines.
- Bisect the two angles.
- The Bisecting lines should be extended to intersect at O.
- O is the centre of the required circle.
- Draw a line perpendicular to any side from centre O to give A.
- With centre O and radius OA draw the required circle.

**HOW TO CONSTRUCT A CIRCLE OR AN ARC OF A GIVEN RADIUS TO TOUCH TWO GIVEN CONVERGING LINES**

**Procedure **

- Draw the given lines AB and AC
- Draw lines parallel to AB and AC at a distance equal to the radius R of the circle.
- Extend the lines to intersect at O.
- Draw a line perpendicular to AB or AC from O.
- With centre O, and radius OD draw the arc to touch the two converging lines.

**EVALUATION**

- Draw a tangent to a circle of radius 40mm from a point ‘P ‘80mm outside the circle.
- With the aid of compasses and a ruler construct angle 600 and 300

**READING ASSIGNMENT**

Read more on construction of tangents.

- MELROSE, Basic Science and Technology, book 2 page 73-76
- NERDC, Basic technology for JSS book 2, page 44-45.

**WEEKEND ASSIGNMENT**

- The angle that FC makes when constructed perpendicular with line AB is _______ (a) 1800 (b) 2700 (c) 900 (d) 1200
- The line FC is called __________ (a) vertical (b) perpendicular (c) Horizontal (d) incline
- Which of the following drawing materials cannot be used to construct a straight line? (a) Compass (b) protractor (c) Ruler (d) pencils
- Angles that sum up to 1800 is called __________ (a) supplementary (b) complementary (c) Reflex (d) obtuse
- The line for all visible outlines is called ____________ (a) Thin continuous line (b) Thick continuous line (c) short dashes (d) Zig – Zag lines.

**THEORY **

- Draw a tangent to a circle of radius 30mm from a point ‘P ‘70mm outside the circle.
- With the aid of compasses and a ruler construct angle 600 and 300.

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