S=p(p−a)(p−b)(p−c)S=\sqrt{p(p-a)(p-b)(p-c)}S=p(p−a)(p−b)(p−c)
p=a+b+c2p=\frac{a+b+c}{2}p=2a+b+c
a=(x1−x2)2+(y1−y2)2a=\sqrt{(x1-x2)^2+(y1-y2)^2}a=(x1−x2)2+(y1−y2)2
b=(x1−x3)2+(y1−y3)2b=\sqrt{(x1-x3)^2+(y1-y3)^2}b=(x1−x3)2+(y1−y3)2
c=(x2−x3)2+(y2−y3)2c=\sqrt{(x2-x3)^2+(y2-y3)^2}c=(x2−x3)2+(y2−y3)2
