Page 27 - ENGINEERING DRAWING

20

2.5 Constructing Triangle

i. Constructing a Triangle given Three sides

Construct a triangle BCA with BC = 3 cm, CA = 5 cm and AB = 4 cm.

CONSTRUCTION

1. Draw a line BC, 6 cm long.
2. Draw an arc of radius 5 cm with C as the centre.
3. Draw an arc of radius 4 cm with B as the centre to cut the arc drawn in Step 2 at A.
4. Join A, the point of intersection of the two arcs to the points B and C.
5. Erase the arcs to obtain the required triangle BCA.

ii. Constructing a Triangle given two sides and an angle.

O
Construct a triangle QRP with QR = 6.5 cm, angle RQP = 60 and QP = 4 cm.
CONSTRUCTION

1. Draw a line QR, 6.5 cm.
2. Mark an angle of 60 by placing the centre of the protractor at the point Q.
o
3. Join the 60 mark and the point Q. Extend the arm QP until it is 4 cm long.
o
4. Join the points R and P to obtain the required triangle QRP.