这是我用三月时间编写的利用余弦定律：知道两条边长（AD两次测得电压幅值）和夹角（用定时器和下降沿中断测夹角）C语言程序。-This is my time to write with the use of March cosine law: that the two side (AD twice the measured voltage amplitude) and the angle (measured with a timer and interrupt falling edge angle)