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**

Geometry

Triangle

Pythagoras

## Check the Answer

But try the problem first…

Answer:\(3\)

PRMO-2012, Problem 7

Pre College Mathematics

## Try with Hints

First hint

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 angle.so 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 ……….

Second Step

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 \(MD=x+1\)

Final Step

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

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

## Other useful links

- https://www.cheenta.com/angles-in-a-circle-prmo-2018-problem-80/
- https://www.youtube.com/watch?v=M_HvBNmPcfU

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