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India Math Olympiad Math Olympiad PRMO

Problem based on Triangle | PRMO-2016 | Problem 10

Try this beautiful problem from PRMO, 2016 based on Triangle You may use sequential hints to solve the problem.

Try this beautiful problem from PRMO, 2016 based on Triangle

Triangle | PRMO | Problem 10


In a triangle ABC right angled at vertex B, a point O is choosen on the side BC such that the circle Y centerer at O of radius OB touches the side AC.Let AB =63 and BC=16 and the radius of Y be the form mn wherw m,n are relatively prime positive integers,find the value of m+n?

  • \(75\)
  • \(80\)
  • \(71\)

Key Concepts


Geometry

Triangle

Circle

Check the Answer


But try the problem first…

Answer:\(71\)

Source
Suggested Reading

PRMO-2016, Problem 10

Pre College Mathematics

Try with Hints


First hint

Problem based on Triangle-  Figure

Given that ABC is a triangle where AB=63 and BC=16 and \(\angle ABC=90^{\circ}\). O is any point on BC.Let OB=\(r\)=radius of the circle.we have to find out the value of \(r\) for \(m+n\).

Now \(\triangle ABC\) is aright angle triangle at\(B\) So using pythagoras theorm \(AC=\sqrt {(AB)^2+(BC)^2}=\sqrt{(63)^2+(16)^2}=65\).now \(\triangle ODC\) is also a right angle triangle as OD radius and AC tangent,can you find out the value of \(r\)?

Can you now finish the problem ……….

Second Step

Problem based on Triangle

Given bc=16,Let OB=\(r\) then OC=\((16- r)\).we have to find out the value of \(r\).if we can show that \(\triangle ABC \sim \triangle ODC\) then we can find out the value of r.can you proof \(\triangle ABC \sim \triangle ODC\)?

Second Step

Problem based on Triangle

In \(\triangle ABC\) & \(\triangle ODC\),

\(\angle ABC=\angle ODC\)

\(\angle C= \angle C\)

Therefore \(\triangle ABC \sim \triangle ODC\)

so we have ….

\(\frac{AC}{OC}=\frac{AB}{OD}=\frac{BC}{AC}\) \(\Rightarrow \frac{65}{16-r}=\frac{63}{r}=\frac{16}{65}\)

Therefore,\(\frac{65}{16-r}=\frac{63}{r}\Rightarrow r=\frac{63}{8}\)=\(\frac{m}{n}\)

Therefore \((m+n)=63+8=71\)

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