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Question

If AD,BE and CF are the medians of ΔABC, then (AD2+BE2+CF2):(BC2+CA2+AB2) is equal to :

A
4:3
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B
3:2
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C
3:4
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D
2:3
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Solution

The correct option is B 3:4

In ABC, AD,BE and CF are medians to respective sides.

So,

BD=DC=12BC

AE=EC=12AC

AF=FB=12AB

By Pythagoras theorem in AFC

AC2=CF2+AF2

AC2=CF2+(12AB)2

AC2=CF2+14AB2

4AC2=4CF2+AB2 ....... (i)

By Pythagoras theorem in BCE

BC2=BE2+EC2

BC2=BE2+(12AC)2

BC2=BE2+14AC2

4BC2=4BE2+AC2 ........ (ii)

By Pythagoras theorem in ADB

AB2=AD2+BD2

AB2=AD2+(12BC)2

AB2=AD2+14BC2

4AB2=4AD2+BC2 ....... (iii)


Adding (i),(ii) and (iii), we get

4AC2+4BC2+4AB2=4AD2+BC2+4BE2+AC2+4CF2+AB2

3AC2+3BC2+3AB2=4AD2+4BE2+4CF2

3(AC2+BC2+AB2)=4(AD2+BE2+CF2)

AD2+BE2+CF2BC2+CA2+AB2=34

(AD2+BE2+CF2):(BC2+CA2+AB2)=3:4

933655_299231_ans_c8008a9dd2c24396a08219c469ba123c.JPG

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