[tex]area = \frac{|A_{x}(By-Cy)+B_{x}(Cy-Ay)+C_{x}(Ay-By)|}{2} [/tex]
A (8,12)
B (3,11)
C (1,7)
[tex]area = \frac{|8(11-7)+3(7-12)+1(12-11)|}{2} [/tex]
[tex]area = \frac{|8(4)+3(-5)+1(1)|}{2} [/tex]
[tex]area = \frac{|32-15+1|}{2} [/tex]
[tex]area = \frac{|18|}{2} [/tex]
[tex]\boxed{area = 9}[/tex]
