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Triangle ABC has altitudes AD, BE, and CF. If  AD=14, BE=16, and  CF is a positive integer, then find the largest possible value of  CF.

 

Ive tried drawing things out but don't know how to figure it out. If anyone can help that would be great.

 Aug 14, 2024
 #2
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Given that triangle ABC has altitudes AD=14, BE=16, and CF=h, where h is a positive integer, we need to find the largest possible value of h.

 

### Step 1: Use the area formula with altitudes


The area of triangle ABC can be expressed in terms of the altitudes and the corresponding sides:

 

Area=12×a×ha=12×b×hb=12×c×hc

 

where ha=AD, hb=BE, and hc=CF=h, and a, b, and c are the lengths of the sides opposite the vertices A, B, and C, respectively.

 

### Step 2: Express the sides in terms of the area and altitudes


Let the area of triangle ABC be denoted as K. Then:

 

K=12×a×14=7a


K=12×b×16=8b


K=12×c×h=12ch

 

### Step 3: Equate the expressions for the area K


From the first two equations:

 

7a=8ba=8b7

 

Using the equation for K involving h:

 

7a=12ch

 

Substitute a=8b7 into the equation:

 

7(8b7)=12ch

 

Simplify:

 

8b=12ch

 

Multiply both sides by 2:

 

16b=ch

 

Thus:

 

h=16bc

 

### Step 4: Maximize h


We aim to maximize h=16bc, where b and c are positive integers.

 

Recall that K=7a=8b=12ch. We want to maximize h, so:

 

c=16bh

 

To maximize h, minimize c. Since b=7, a=8, choose b=7 and c=1 which gives:

 

h=16×71=112

 

However, since b=gcd(7,8), choose b=7 for simplicity. So:

 

\[
K = 112, h = 1
]


Thus:

 

h112

 

### Final Answer:

 

Since h=112, the maximum value for the given maximum number is 112.

 Aug 16, 2024

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