23. An aeroplane takes 17 hours to fly a distance of 15419 km. How far does it fly
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Its perimeter is 21 cm because we are given with all sides of triangle ABC.
The perimeter of triangle DEF is 1
Sl
It is given that , In Δ AB C , D, E and F are mid points of AB, BC and CA respectively.
Also, AB=6 cm, BC= 7.2 cm, and CA= 7.8 cm
Keep in mind :
Line segment joining the mid point of two sides of triangle is parallel to third side and is half of it.
So, DE ║AC,and DE= \frac{AC}{2}
EF║AB, and FE= \frac{AB}{2}
DF║BC ,and D F= \frac{BC}{2}
DF= \frac{7.2}{2}=3.6 cm,
DE=\frac{7.8}{2}=3.9 cm,
EF=\frac{6}{2}=3 cm,
So, Perimeter of Δ ABC=AB +BC+CA
= 6 + 7.8 +7.2
= 21 cm
Perimeter of ΔDEF=DE +E F +D F
=3 +3.6 +3.9
= 6.6 +3.9
= 10.5 cm
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