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Question

In Fig. 7.223, D is the mid-point of side BC and AEBC. If BC = a AC=b, AB=c, ED=z, AD = p and AE =h, prove that:


(i) b2=p2+ax+a24
(ii) c2=p2+ax+a24
(iii) b2+c2=2p2+a24

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Solution

i)

https://s3mn.mnimgs.com/img/shared/userimages/mn_images/image/a1(635).png

D is the mid point of BC and AE⊥BC.

In right ∆ ABE,

A B squared equals A E squared plus B E squared … (1) (Pythagoras Theorem)

In right ∆ ADE,

A D squared equals A E squared plus E D squared … (2) (Pythagoras Theorem)

From (1) and (2), we get

A B squared equals A D squared minus E D squared plus B E squared A B squared equals A D squared minus E D squared plus open parentheses B D minus D E close parentheses squared A B squared equals A D squared minus E D squared plus B D squared minus 2 B D cross times D E plus E D squared A B squared equals A D squared plus B D squared minus 2 B D cross times D E A B squared equals A D squared plus open parentheses fraction numerator B C over denominator 2 end fraction close parentheses squared minus 2 open parentheses fraction numerator B C over denominator 2 end fraction close parentheses cross times D E A B squared equals A D squared plus fraction numerator B C squared over denominator 4 end fraction minus B C cross times D E

Since, AB= c, AD= p, BC = a, DE = x ……………….(Given)

Substituting the above values, we get

c squared equals p squared minus a x plus a squared over 4


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