CBSE Class 7 Mathematics Lines And Angles Notes

CBSE Class 7 Lines and Angles Concepts. Learning the important concepts is very important for every student to get better marks in examinations. The concepts should be clear which will help in faster learning. The attached concepts made as per NCERT and CBSE pattern will help the student to understand the chapter and score better marks in the examinations.

Lines and Angles

5.1Lines

A line segment has two end points. If we extend the two end points in either direction endlessly, we get a line. Thus, we can say that a line has no end points. 

Ray: A ray has one end point

Example:

(i) shows a line segment, (ii) shows a line and (iii) is that of a ray.

5.2 Angles

An angle is formed when lines or line segments meet.

Example:

(i) line segments AB and BC intersect at B to form angle ABC, and again line segments BC and AC intersect at C to form angle ACB and so on. Whereas, in (ii) lines PQ and RS intersect at O to form four angles POS, SOQ, QOR and ROP. An angle ABC is represented by the symbol

ii) Right angle: An angle whose measure is 90 degrees. The following is a right angle.

iii) Obtuse angle: An angle whose measure is more than 90 degrees but less than 180 degrees. Thus, it is between 90 degrees and 180 degrees. The following are obtuse angle.

iv)Straight angle: An angle whose measure is 180 degrees. Thus, a straight angle look like a straight line. The following is a straight angle.

v)Reflex angle: An angle whose measure is more than 180 degrees but less than 360 degrees. The following is a reflex angle.

vii)Complementary angles: Two angles whose measures add to 90 degrees. Angle 1 and angle 2 are complementary angles because together they form a right angle.

Note : Angle 1 and angle 2 do not have to be adjacent to be complementary as long as they add up to 90 degrees

viii) Supplementary angles: Two angles whose measures add to 180 degrees. The following are supplementary angles. Angles, forming a pair of supplementary angles, need not to be adjacent angles

ix) Vertically angles: Angles that have a common vertex and whose sides are formed by the same lines. The following angles are pair of vertically opposite angles:

When two lines  l₁ and l₂ are crossed by a third line l­₃ (Transversal), 8 angles are formed. Take a look at the following figure

Angles 3,4,5,8 are interior angles

Angles 1,2,6,7 are exterior angles

x) Alternate interior angles: Pairs of interior angles on opposite sides of the transversal.

For instance, angle 3 and angle 5 form a pair of alternate interior angles. Angle 4 and angle 8 form a pair of alternate interior angles.

xi) Alternate exterior angles: Pairs of exterior angles on opposite sides of the transversal.Angle 2 and angle 7 form a pair of alternate exterior angles. Similarly <1 and < 6 also

 xii) Corresponding angles: Pairs of angles that are in similar positions.Angle 3 and angle 2 form a pair of corresponding angles. Angle 5 and angle 7 form a pair of corresponding angles