Just use the unequal relationship between the sides of the triangle (after any two sides of the triangle, it is greater than the third side)
∵AP+BP & gt; abdominal muscle
BP+PC & gt; B.C.
PC+AP & gt; alternating current
The above three formulas add up to get.
2 *(AP+BP+CP)& gt; (ab+bc+ca)
Namely: (pa+pb+pc)> 1/2(ab+bc+ac)