NCERT Class 7 Maths Practical Geometry. Download NCERT Chapters and Books in pdf format. Easy to print and read. Copies of these textbooks may be downloaded and used as textbooks or for reference. Refer to other chapters and books at other links (NCERT now providing you soft copies of all textbooks of all subjects from class first to twelfth online).
You are familiar with a number of shapes. You learnt how to draw some of them in the earlier classes. For example, you can draw a line segment of given length, a line perpendicular to agiven line segment, an angle, an angle bisector, a circle etc. Now, you will learn how to draw parallel lines and some types of triangles.
10.2 CONSTRUCTION OF A LINE PARALLEL TO A GIVEN LINE,THROUGH A POINT NOT ON THE LINE
Let us begin with an activity (Fig 10.1)
(i) Take a sheet of paper. Make a fold. This fold represents a line l.
(ii) Unfold the paper. Mark a point A on the paper outside l.
(iii) Fold the paper perpendicular to the line such that this perpendicular passes through A. Name the perpendicular AN.
(iv) Make a fold perpendicular to this perpendicular through the point A. Name the new perpendicular line as m. Now, l || m. Do you see ‘why’?Which property or properties of parallel lines can help you here to say that lines l and m are parallel.
You can use any one of the properties regarding the transversal and parallel lines to make this construction using ruler and compasses only.
Step 1 Take a line ‘l ’ and a point ‘A’ outside ‘l ’ [Fig10.2 (i)].
Step 2 Take any point B on l and join B to A [Fig 10.2(ii)].
Step 3 With B as centre and a convenient radius, draw an arc cutting l at C and BA at D [Fig 10.2(iii)].
Step 4 Now with A as centre and the same radius as in Step 3, draw an arc EF cutting AB at G [Fig 10.2 (iv)]
Step 5 Place the pointed tip of the compasses at C and adjust the opening so that the pencil tip is at D [Fig 10.2 (v)].
Step 6 With the same opening as in Step 5 and with G as centre, draw an arc cutting the arc EF at H [Fig 10.2 (vi)].
Step 7 Now, join AH to draw a line ‘m’ [Fig 10.2 (vii)].
Note that ∠ABC and ∠BAH are alternate interior angles. Therefore m|| l
Please refer to attached file for NCERT Class 7 Maths Practical Geometry