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In order to divide a line segment internally is a given ratio m: n, where both m and n are positive integers,
We follow the following steps:
(i) Draw a line segment AB of given length by using a ruler.
(ii) Draw and ray AX making an acute angle with AB.
(iii) Along AX mark off (m + n) points A1, A2,..., Am+n such that AA1 = A1A2 = ....= Am+n+Am+n.
(iv) Join B Am+n
(v) Through the point Am draw a line parallel to Am+n B by making an angle equal to ∠AAm + n Bat Am.
Suppose this line meets AB at a point P.
The point P so obtained is the required point which divides AB internally in the ratio m:n.
question 1. To divide a line segment in a given ratio 3 : 2.
Solution: Given a line segment AB, we want to divide it in the ratio 3 : 2.
Steps of construction:
1. Draw any ray AX, making an acute angle with AB.
2. Locate 5(= m + n) points A1,A2,A3,A4, and A5 on AX so that
AA1 = A1A2 = A2A3 = A3A4 = A4A5.
3. Join BA5.
4. Through the point A3 (m = 3), draw a line parallel to A5B (by making an angle equal to ∠AA5B) intersecting AB at the point C
Then, AC : CB = 3 : 2
Let us see how this method gives us the required division.
Since A3C is parallel to A5B therefore,
(By the basic proportionality theorem)
By construction, Therefore, .
This shows that C divides AB in the ratio 3 : 2
We now use the above ideas of construction for constructing a triangle similar to a given triangle above whose sides are in a given ratio with the corresponding sides of the given triangle.
Question 2. Construct a triangle of sides 4 cm, 5 cm and 6 cm then construct a triangle similar to it whose sides are 2/3 of the corresponding sides of it.
Solution: Steps of construction:
1. Take BC = 6 cm. Let ∠CBX be any acute angle (< 90°).
2. Mark the three points B1,B2,B3 (number of parts should be larger of the 2 and 3 in 2/3) such that BB1 = B1B2 = B2B3.
3. Join B3C and draw a line through B2 (the second point) parallel to B3C which meets BC at C′.
4. Draw C'A' parallel to CA which intersects AB at A′.
Do solve NCERT text book for class 10 maths with the help of Physics Wallah NCERT solutions for class 10 maths.