Class 7 Math Solution WBBSE Geometry Chapter 1 Revision Of Old Lesson Exercise 1 Solved Problems
Question 1. Draw a line segment AB of length 10 cm. Bisect the line segment AB with the help of a compass and measure each part.
Solution: Method of construction:
1. I draw a line segment AB of length 10 cm
2. With A as a centre and with a radius more than half the length of AB, two arcs are drawn on either side of the line segment AB.
3. Again with B as the centre and with the radius two arcs are drawn on either of the line segment AB such that these two arcs intersect previous arcs at P and Q respectively. P and Q are joined with a scale and a pencil to get the midpoint O’ of the line segment AB.
Thus AO = OB = 5 cm.
Wbbse Class 7 Maths Solutions
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Question 2. Draw an angle of 75° with the help of a protractor, then bisect the angle with the help of a scale, pencil and compass.
Solution:
Steps for drawing the angle:
1. I draw an angle ∠ABC where ∠ABC = 75°
2. With centre B and with any radius, I draw an arc cutting the arms AB and BC of the ∠ABC at P and Q respectively.
3. With centre P and radius equal to more than half the length PQ, an arc is drawn.
4. Again with centre Q and with the same radius, an arc is drawn to the previous arc at R. Points B and R are joined and produced. The ray BR is the bisector of ∠ABC.
Thus ∠ABR=∠CBR = 37-5°
Wbbse Class 7 Maths Solutions
Question 3. With the help of a scale, pencil and compass, draw a line segment perpendicular to a line from a point outside it.
Solution:
1. A straight line PQ is drawn and a point A is taken outside the straight line
2. I take any point T on the side of the straight line PQ opposite to point A.
3. With centre A and a radius AT, I draw an arc which cuts the straight line PQ at R and S.
4. With centres R and S and a radius equal to more than half of the line segment RS, two arcs are drawn on the side of the line PQ opposite to A, where two arcs intersect at B.
5. points A and B are joined with a scale and pencil. The line segment AB; cuts the straight line PQ at O.
∴ AO ⊥ 
and ∠AOP =∠AOQ = 90°
