in this section we'll discuss lines and angles now to start off with if I take a point and if I move the point freely like this you can see the path followed here this is called the curved line now if I take a point when this point is moved without changing the direction like this I got a straight line so now for a line part of a line with let's say two end points like this is called a line segment now if I take part of a line with one end point and the other one like this so I'm marking an arrow Mark over here this is called array so these are things which all of you know I'm just revising it when there are uh two end points we call it a line segment one end point we call it a ray so let's define let's look at Angles next how do we get an angle very very simple right two rays emerging from a point like this you get an angle one more way of looking at that is take the first Ray rotate like this so I get the same angle so angles are formed like this very simple right two rays will be part of it there will be a common point now we'll see classification of polygons now based on the number of sides or number of vertices the polygons are named like this when there are three sides or three vertices like this this is a triangle when there are four sides or four vertices it's called a quadrilateral when there are five sides like this or five vertices it's a pentagon now if it is uh six sides and six vertices it's a hexagon seven it will be a heptagon eight it will be an octagon like this uh polygons can be named based on sides or the vertices now next thing we'll understand is what are diagonals now a diagonal is a line segment connecting the two non-consecutive vertices of a polygon this is easy to understand in a diagram so just uh to help you understand let's take a quadrilateral AB CD in this case A and C are two non-consecutive vertices so a c is a diagonal B and D are non-con so BD is a diagonal so here AC and BD are diagonals in a pentagon pqrst like this if you join all the non-consecutive vertices you will get the diagonals here so in this case p r PS TQ TR R and Qs they are the diagonals you can just take a look at it P and PS TQ and TR and Qs are the diagonals for this polygon now pqrst so now we'll also understand more about diagonals as part of uh this discussion so diagonals are nothing but line segment joining or connecting the two non-consecutive vertices of a polygon next we'll understand the difference between convex polygons and concave polygons so in a diagram itself if you if I just draw convex and concave polygons here a convex polygon will look like this an example can be this this hexagon or uh this quadrilateral these two are convex polygons we'll understand the difference now a concave polygon I can show you this is a concave polygon or this is uh a concave polygon now in terms of diagonals if you want me to explain what are convex and concave polygons in a convex polygon like these two no portions of diagonals will lie in the exterior so here if if you consider the diagonals in this diagram you can just see it here or here so these diagonals are in in the interior or no part of it is actually in the exterior right so exterior is the unshaded region here now in the second part of it in concave polygons the diagonals part of diagonals portion of diagonals can be outside also as you can see in these two so so convex polygons and concave polygons are easy to identify as part of this chapter this discussion we will only deal with convex polygons next we'll see regular polygons and irregular polygons it's very simple regular polygon is both equiangular and equilateral that means uh they'll have angles will be equal and sides will be equal and if it's not like that then the polygon is an irregular polygon just to differentiate between the two let's look at TP now a square like this where the angles are equal and sides are equal is a regular polygon but a rectangle like this where even though the angles are equal but sides are not equal it's an irregular polygon now equilateral triangle like this where the sides are equal and angles are equal is a regular polygon and right angle triangle like this where the sides are not equal is an irregular polygon now if you see these two diagrams this is a regular hexagon because here all the Ang sides are equal all angles are equal and this is not a regular hexagon this is an irregular polygon because here all the six sides are not equal all the six angles are not equal so because of this is a regular diagram this is a regular polygon this is an irregular one so it's it's very easy to differentiate that is when the the sides are equal angles are equal it's called a regular polygon next we will look at quadrilaterals specifically lot of properties of quadrilaterals different types of quadrilaterals