Because A 1A = 2AC, triangle A 1AB = 2, triangle ABC = 2. Similarly, triangle ACC 1 = BB 1C = 2, and because A 1A = 2AC, triangle A 1AC 1 = 2. 4 * 3+2 * 3+ 1 = 19, triangle a1BAC1= s1=19.
So it can be seen that the triangle area is enlarged by 19 times every time.
S5= 19^5=2476099
The topic says that this formula is always less than zero, so the maximum value of f(x) is < 0, but this sentence is not rigo