Ceva or Menelaus?

Geometry Level 2

In triangle A B C , ABC, E E lies on A C AC and F F lies on A B AB such that F E B C . FE \parallel BC. P P is the intersection point of B E BE and C F , CF, and extension of A P AP meets B C BC at point D . D. Given that A E = 2 , C E = 3 , A D = 7 , AE=2, \quad CE=3, \quad AD=7, find length of A P . AP.


The answer is 4.

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

2 solutions

Chan Tin Ping
Jan 7, 2018

F E / / B C \because FE//BC , A F F B = E A C E \therefore \frac{AF}{FB}=\frac{EA}{CE} . Apply Ceva theorem with A B C \triangle ABC and point P P , we get A F F B × B D D C × C E E A = 1 B D = D C \begin{aligned} \frac{AF}{FB}× \frac{BD}{DC}× \frac{CE}{EA}&=1 \\ BD&=DC \end{aligned} Apply Menelaus theorem with A C D \triangle ACD and line B P E BPE , we get A E E C × C D + D B B D × D P P A = 1 2 3 × 2 1 × D P P A = 1 4 D P = 3 P A \begin{aligned} \frac{AE}{EC}× \frac{CD+DB}{BD}× \frac{DP}{PA}&=1 \\ \frac{2}{3}× \frac{2}{1}× \frac{DP}{PA}&=1 \\ 4DP&=3PA \end{aligned} A D = A P + P D 4 A D = 4 A P + 4 P D 28 = 4 A P + 3 A P A P = 4 \begin{aligned} AD&=AP+PD \\ 4AD&=4AP+4PD \\ 28&=4AP+3AP \\ AP&=\large 4 \end{aligned}

Patrick Bamba
Jan 15, 2018

First, we notice that since F E FE is parallel to B C BC , then A F E \triangle AFE is similar to A B C \triangle ABC , and thus, A F / F B = A E / E C = 2 / 3 AF/FB = AE/EC = 2/3 . Now, we use mass points.

Let m A = 3 m_A = 3

We get m B = m C = 2 m_B = m_C = 2

m D = m B + m C = 4 m_D = m_B + m_C = 4

A P / A D = m D / ( m A + m D ) = 4 / 7 AP/AD = m_D/(m_A + m_D) = 4/7

A P = 4 \boxed{AP = 4}

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...