Olympiad Maths Prep

Track / Stage 6 / 325 of 400 #1325 of 2000

Problem 1325

National olympiad, first round
Geometry Difficulty 6.5 Find the answer

Let ABCABC be a triangle such that AB=7|AB|=7, BC=8|BC|=8, AC=6|AC|=6. Let DD be the midpoint of side [BC][BC]. If the circle through AA, BB and DD cuts ACAC at AA and EE, what is AE|AE|?

$
\textbf{(A)}\ \dfrac 23
\qquad\textbf{(B)}\ 1
\qquad\textbf{(C)}\ \dfrac 32
\qquad\textbf{(D)}\ 2
\qquad\textbf{(E)}\ 3
$

Official solution

1. Identify the given information and the goal:
- We have a triangle ABCABC with sides AB=7AB = 7, BC=8BC = 8, and AC=6AC = 6.
- DD is the midpoint of BCBC, so BD=DC=82=4BD = DC = \frac{8}{2} = 4.
- We need to find the length of AEAE where EE is the point where the circle through AA, BB, and DD intersects ACAC again.

2. Apply the Power of a Point theorem:
- The Power of a Point theorem states that for a point CC outside a circle, if a line through CC intersects the circle at points EE and AA, then CECA=CDCBCE \cdot CA = CD \cdot CB.

3. Substitute the known values into the Power of a Point equation:
CECA=CDCB CE \cdot CA = CD \cdot CB
CE6=48 CE \cdot 6 = 4 \cdot 8

4. **Solve for CECE:**
CE6=32 CE \cdot 6 = 32
CE=326=163 CE = \frac{32}{6} = \frac{16}{3}

5. **Determine AEAE using the segment subtraction:**
- Since EE is on ACAC, we have AE=ACCEAE = AC - CE.
AE=6163 AE = 6 - \frac{16}{3}
AE=183163=23 AE = \frac{18}{3} - \frac{16}{3} = \frac{2}{3}

The final answer is 23\boxed{\frac{2}{3}}

Source: NuminaMath-1.5, licensed Apache-2.0. Statement and solution reproduced as published; topic, difficulty and ordering added by this site.