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# In Fig. 6.57, D is a point on hypotenuse AC of triangle ABC, such that BD perpendicular AC, DM perpendicular BC and DN perpendicular AB. Prove that : DM ^2 = DN . MC

Q2   In Fig. 6.57, D is a point on hypotenuse AC of triangle ABC, such that BD $\perp$ AC, DM $\perp$ BC and
DN $\perp$ AB. Prove that : $DM^2 = DN . MC$

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Given :  D is a point on hypotenuse AC of D ABC, such that BD $\perp$ AC, DM $\perp$ BC and  DN $\perp$ AB.Also DN || BC, DM||NB

$\angle CDB=90 \degree$

$\Rightarrow \angle 2+\angle 3=90 \degree.............................1$

In $\triangle$ CDM, $\angle 1+\angle 2+\angle DMC=180 \degree$

$\angle 1+\angle 2=90 \degree.......................2$

In $\triangle$ DMB, $\angle 3+\angle 4+\angle DMB=180 \degree$

$\angle 3+\angle 4=90 \degree.......................3$

From equation 1 and 2, we get $\angle 1=\angle 3$

From equation 1 and 3, we get $\angle 2=\angle 4$

In $\triangle DCM\, \, and\, \, \triangle BDM,$

$\angle 1=\angle 3$

$\angle 2=\angle 4$

$\triangle DCM\, \, \sim \, \, \triangle BDM,$     (By AA)

$\Rightarrow \frac{BM}{DM}=\frac{DM}{MC}$

$\Rightarrow \frac{DN}{DM}=\frac{DM}{MC}$           (BM=DN)

$\Rightarrow$$DM^2 = DN . MC$

Hence proved

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