Eventually distributed points in any direction can called  line.

Eventually distributed points in particular direction  can called   straight line.

See below fig to understand different type of lines. ###### angeles

When two lines are intersect  then there will be one corner formed this corner is called vertex. In the above fig1-e two line AB and CD are intersecting at the point O. Due to the intersection  of two lines there are four angles. Try to name that four angles.

###### complementary angles

If the sum of two angle are 90º then the are called complementary angles.

Now try to answer following questions.

1. Can two acute angles be complement to each other?
2. can two obtuse angles be complement to each other?
3. Can two right angles be complement to each other?

From the below figure identify which pair of angles are complementary.

Supplementary angles : If the sum of 2 angles are equal to 180°, then that angles are called Supplementary angles.

1. Can two obtuse angles be supplementary ?
2. Can two acute angles be supplementary ?
3. Can two right angles be supplementary ?

Check for some exercises in the test book.

Adjacent angles: If two angles are adjacent angles then they have a common vertex .a common arm and there non -common arm are the different side of the common arm. In the below figure-2 we can see a adjacent angles. Here the angle ∠ABD and ∠DBC are adjacent angle. But also note that ∠ ABC is not adjacent angle. More over when there is two adjacent angle, then the sum is always equal to the angle formed by two non-common arms

that is  ∠ABD+∠CBD=∠ABC

###### LINEAR PAIR OF ANGLE

If the non-common arm of an adjacent angle are opposite ray the angles are called linear pair of angle. As shown in the fig3, AB and BC are non common arm and the angle ABD and angle CBD are linear pair of angle. Linear pair are supplementary. TRy to answer the following questions

1. Can two obtuse angles be linear pair ?
2. Can two acute angles be linear pair ?
3. Can two right angles be linear pair ?

Now try to do some exercises from textbook