~~啊就是英文啊系統你是在徵求什麼~~
The most popular language in the world. If you understand English, it is assumed that you can communicate with >20% of the population in the world.
世界上最流行的語言。如果您懂英語,您可以與世界上超過 20% 的人口進行交流。
https://i.imgur.com/huGjddY.png
h²=a²-x²,h²=c²-(b-x)²
a²-x²=c²-(b-x)²
a²-x²=c²-b²+2bx-x²
a²=c²-b²+2bx
2bx=a²+b²-c²
x=a²+b²-c²/2b
cos c=x/a=a²+b²-c²/2ab
c²=a²+b²-2ab cos c