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Let ABC be an acute angled triangle whos...

Let ABC be an acute angled triangle whose orthocentre is at H. If altitude from A is produced to meet the circumcircle of triangle ABC at `D` , then prove `H D=4RcosBcosC`

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`/_BHN` and `/_BDN` are congurent
`HN=ND=2RcosBcosC`
`HD=2HN`
`2*2RcosBcosC`
`4RcosBcosC`.
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