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Problem based on Triangle | PRMO-2012| Problem 7

Try this beautiful problem from PRMO, 2012 based on Triangle.

Triangle | PRMO | Problem 12

In \(\triangle ABC\) we have \(AC=BC=7\) and \(AB=2\).Suppose that \(D\) is a point on line \(AB\) such that \(B\) lies between \(A\) and \(D\) and \(CD=8\) .what is the length of the segment \(DB\)?

  • \(5\)
  • \(3\)
  • \(7\)

Key Concepts




Check the Answer


PRMO-2012, Problem 7

Pre College Mathematics

Try with Hints

Problem based on Triangle

Given that \(AC=BC=7\) & \(CD=8\).we have to find out \(BD\).Let \(BD=x\).we draw a perpendicular from \(C\) to \(AB\) at the point \(M\).Therefore clearly \(\triangle CMB\) & \(\triangle CMD\) are right if we can find out the value of \(CM\) from the \(\triangle CMB\) then we can find out the value \(BD\) from the \(\triangle CMD\)

Can you now finish the problem ..........

Problem based on Triangle

From the above diagram,In \(\triangle CMB\) we can say that \(CM=\sqrt{49-1}=4\sqrt 3\)

Given \(AB=2\) and \(M\) is the mid point of \(\triangle ABC\) (As AC=BC=7,Isosceles triangle),

Therefore \(BM=1\), So \(MD=x+1\)

Figure of the Problem

From the \(\triangle CMD\), \((X+1)^2+(4\sqrt 3)^2=64\) \(\Rightarrow x=3,-5\)

we will take the positive value ,so \(BD=3\)

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