Try this beautiful Problem on Sum of Sides of Triangle from Triangle from Prmo-2018, Problem 17.

## Sum of Sides of Triangle – PRMO, 2018- Problem 17

Triangles $\mathrm{ABC}$ and $\mathrm{DEF}$ are such that $\angle \mathrm{A}=\angle \mathrm{D}, \mathrm{AB}=\mathrm{DE}=17, \mathrm{BC}=\mathrm{EF}=10$ and $\mathrm{AC}-\mathrm{DF}=12$

What is $\mathrm{AC}+$ DF ?

,

- \(28\)
- \(30\)
- \(21\)
- \(26\)
- \(26\)

**Key Concepts**

Geometry

Triangle

## Suggested Book | Source | Answer

#### Suggested Reading

Pre College Mathematics

#### Source of the problem

Prmo-2018, Problem-17

#### Check the answer here, but try the problem first

\(30\)

## Try with Hints

#### First Hint

In \(\triangle ABC\) & \(\triangle DEF\), given that \(\angle A\)=\(\angle D\) & \(AB=DE\)=$17$ . $BC = EF = 10 $ and $AC â€“ DF = 12.$ we have to find out $AC+DF$.

According to the question Let us assume that the point A coincides with D, B coincides with E. Now if we draw a circle with radius 10 and E(B) as center ….

Can you finish the problem?

#### Second Hint

Let M be the foot of perpendicular from B(E) to CF. So BM = 8. Hence $\mathrm{AM}=\sqrt{17^{2}-8^{2}}=\sqrt{(25)(9)}=15$

#### Third Hint

Hence $AF = 15 â€“ 6 = 9$ & $AC = 15 + 6 = 21$

So $AC + DF = 30$

## 2 replies on “Sum of Sides of Triangle | PRMO-2018 | Problem No-17”

We can directly apply Cosine law

yes we can..

Google