Parallel and Intersecting Lines | FIO

Question 1

List all the linear pairs and vertically opposite angles you observe in Fig. 5.3:

Question diagram 1Question diagram 2
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Solution

When two lines cross each other, they form different types of angles.

Step 1 — Identifying Linear Pairs

Linear pairs are two angles that are next to each other. They form a straight line together. The sum of their measures is always 180 degrees.

Let us look at the diagram. Line ll and line mm intersect. We can find pairs of angles that form a straight line.

  • Angles a\angle a and b\angle b are next to each other on line mm. They form a straight line.
  • Angles b\angle b and c\angle c are next to each other on line ll. They form a straight line.
  • Angles c\angle c and d\angle d are next to each other on line mm. They form a straight line.
  • Angles d\angle d and a\angle a are next to each other on line ll. They form a straight line.

Diagram 1

Step 2 — Identifying Vertically Opposite Angles

Vertically opposite angles are formed when two lines cross. They are directly opposite each other. These angles are always equal in measure.

Let us look at the diagram again. Line ll and line mm cross each other. We can find angles that are opposite to each other.

  • Angle a\angle a is opposite to angle c\angle c.
  • Angle b\angle b is opposite to angle d\angle d.

Diagram 2

Answer

Linear Pairs: a\angle a and b\angle b, b\angle b and c\angle c, c\angle c and d\angle d, d\angle d and a\angle a. Pairs of Vertically Opposite Angles: b\angle b and d\angle d, a\angle a and c\angle c.

More questions in FIO

Q1

List all the linear pairs and vertically opposite angles you observe in Fig. 5.3:

Q2

Draw some lines perpendicular to the lines given on the dot paper in Fig. 5.10.

Q3

In Fig. 5.11, mark the parallel lines using the notation given above (single arrow, double arrow etc.). Mark the angle between perpendicular lines with a square symbol.

(a) How did you spot the perpendicular lines?

(b) How did you spot the parallel lines?

Q4

In the dot paper following, draw different sets of parallel lines. The line segments can be of different lengths but should have dots as endpoints.

Q5

Using your sense of how parallel lines look, try to draw lines parallel to the line segments on this dot paper.

(a) Did you find it challenging to draw some of them? (b) Which ones? (c) How did you do it?

Q6

In Fig. 5.13, which line is parallel to line a — line b or line c? How do you decide this?

Q7

Can you draw a line parallel to ll, that goes through point A? How will you do it with the tools from your geometry box? Describe your method.

Q8

Find the angles marked below.

Q9

Find the angle represented by aa.

Q10

In the figures below, what angles do xx and yy stand for?

Q11

In Fig. 5.33, ABC=45\angle ABC = 45^\circ and IKJ=78\angle IKJ = 78^\circ. Find angles GEH\angle GEH, HEF\angle HEF, FED\angle FED

Q12

In Fig. 5.34, ABAB is parallel to CD and CD is parallel to EF. Also, EA is perpendicular to AB. If BEF=55\angle\text{BEF} = 55^\circ, find the values of xx and yy.

Q13

What is the measure of angle NOP\angle\text{NOP} in Fig. 5.35?

[Hint: Draw lines parallel to LM and PQ through points N and O.]

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