i) Legs of the table, railway track, edges of the scale
ii) Adjacent sides of a Board, Cross bars of windows, Adjacent sides of the textbook
iii) Cross bars of windows, Ladder, blades of a scissor.

Construction:
(i) Placed the centre of the protractor at the vertex '0', Lined up the ray \(\overline { OP } \) with the 0° line. Then draw and labelled a point Qat 90° mark on the
(a) inner scale (anticlockwise) and
(b) outer scale (clockwise)
(ii) Removed the protractor and draw \(\overline { OQ } \) to complete the angle.
Now < O = < POQ == < QOP= 90°.

(i) \(\overline{EF}and\overline{GH},\overline{CD}and\overline{AB}\)
(ii) \(\overline{CD}and\overline{EF},\overline{AB}and\overline{EF},\overline{CD}and\overline{GH},\overline{AB}and\overline{GH}\)
(iii) P, Q, R and S

(i) and (iv) are complementary angles
(ii) and (iii) are non-complementary angles

Paralell line:
\( \overline{\mathrm{AB}} \ \text{and}\)  \( \overline{\mathrm{DC}},\)
\( \overline{\mathrm{AD}} \ \text{and}\) \(\overline{\mathrm{BC}},\)
\(\overline{\mathrm{DC}} \text { and } \overline{\mathrm{HG}}, \)
\(\overline{\mathrm{AD}} \text { and } \overline{\mathrm{EH}},\)
\( \overline{\mathrm{AE}} \text { and } \overline{\mathrm{DH}}, \)
\( \overline{\mathrm{DH}} \text { and } \overline{\mathrm{GG}}\)
Intersecting lines:
\(i) \ \overline{\mathrm{AB}}, \overline{\mathrm{AE}}, \overline{\mathrm{AD}}\\ ii) \ \overline{\mathrm{DA}}, \overline{\mathrm{DH}}, \overline{\mathrm{DC}}\\ iii) \ \overline{\mathrm{CB}}, \overline{\mathrm{CG}}, \overline{\mathrm{CD}}\\ iv)\ \overline{\mathrm{HD}}, \overline{\mathrm{HG}}, \overline{\mathrm{HE}}\\ v) \ \overline{\mathrm{EA}}, \overline{\mathrm{EH}}_{, . .}\)

i), iii) are obtuse angles

Complementary angle of 90º = 90º - 90º = 0º

Complementary angle of 26º = 90º - 26º = 64º 

obtuse angle

straight angle

Parallel and Perpendicular lines