C语言算法-求两直线夹角计算公式

设两直线夹角为θ,l1的倾角为α,l2的倾角为β.

则:tanα=( y2-y2 )/( x2-x1 ) tanβ=( y4-y3 )/( x4-x3 )

根据两直线夹角公式得:

tanθ= ( | tanα-tanβ | ) / ( 1 + tanα*tanβ )

所以

θ = arc tan[( | tanα-tanβ | ) / ( 1 + tanα*tanβ )]

最后分别把 tanα , tanβ 代入.

下附一段测试代码:

#include <math.h>
#include <stdio.h>
//编写:GUO (QQ:349384061)
void main( void )
{
   double pi = 3.1415926535;
   double tan1,tan2;
   double tan3,angle;
   tan1 = tan(pi * 30 / 180);
   tan2 = tan(pi * 120 / 180);
   tan3 = fabs(tan1 - tan2) / (1 + tan1 * tan2);
   angle = atan(tan3) / pi * 180;
   printf("tan1:%f
",tan1);
   printf("tan2:%f
",tan2);
   printf("tan3:%f
",tan3);
   printf("angle:%f
",angle);
}