Introduction to learn alternate angles:

Alternate Angles - Alternate angles are formed when a transversal cuts two (or more) straight lines.The alternate interior angles are on opposite sides of the transversal line, inside the lines being transversed. Alternate exterior angles are on opposite sides of the transversal line, outside the lines being transversed.

  

Learning alternate angles:

 

As we have learnt earlier that, alternate angles are formed when a transversal cuts two (or more) straight lines. Now, if the transversal cuts two parallel straight lines then the alternate angles formed are equal. Otherwise, if the lines are not parallel to each other, the alternate angles formed differ from each other in their values. The diagrams given below will make the scenario more clear.

1.Unequal  Alternate angles formed by Two Non -parallel lines :-   

                                          :Non parallel lines

Here the angles marked are alternate. Since the lines, which the transversal cuts are non- parallel, they are unequal.

 

2. Equal Alternate angles formed by cutting Parallel Straight lines :-

Parallel lines intersected by transversal

The alternate angles formed in the above figure are formed by cutting two parallel lines. The transversal AB while cutting the parallel lines gives rise to 2 pairs of alternate angles marked as 1,3 ; and 2,4. Moreover angles 1 and 3 are equal; and angles 2 and 4 are also equal. 

 

 

 

learn Important point to remember alternate angle:

 

Its sometimes becomes very confusing to sort out the alternate angles. So, to overcome this a process can be opted. If a  'Z', can be found out in a figure, the thing becomes more clear and vivid. And the angles associated with the 'Z' are alternate angles. Now, if a perfect 'Z' , is formed by 2 parallel straight lines, then the angles are Equal alternate angles. Otherwise if a tilted 'Z' , is formed by 2 non- parallel straight lines and a transversal, then the alternate angles thus formed are non parallel.