Thanks Pangolin14 and Yugoslav
I tackled this in a different way.
I also used co-ordinate geometry. As shown on my pic.
I set the centre of the incircle (since that is what I is) as the origin.
B(-4,-3) and C((4,-3)
I need to find the height of the triangle
Let the equation of the line AB be y= -mx+b where m and b are both positive.
The perpendicular distance of the origin to line AB is the radius, 3.
So I will use the perpendicular distance formula
y= -mx+b
mx + y -b = 0 (0,0)
\(3=\frac{|0+0-b|}{\sqrt{m^2+1}}\\ 3=\frac{b}{\sqrt{m^2+1}}\\ b=3\sqrt{m^2+1} \)
So we have
\(y=-mx+3\sqrt{m^2+1}\\\)
This line passes through the point (4,-3) so substitute
\(-3=-4m+3\sqrt{m^2+1}\\ -3+4m=3\sqrt{m^2+1}\\ 16m^2-24m+9=9(m^2+1)\\ 16m^2-24m+9=9m^2+9\\ 7m^2-24m=0\\ 7m-24=0\\ m=\frac{24}{7}\)
\(b=3\sqrt{m^2+1}\\ b=3\sqrt{(\frac{24}{7})^2+1}\\ b=3*\frac{25}{7}=\frac{75}{7}\\ \text{height of triangle }= \frac{75}{7}+3 = \frac{96}{7}\)
\(\text{Area of triangle ABC = }\frac{1}{2}*8*\frac{96}{7}\\ \text{Area of triangle ABC = }54\frac{6}{7}\;units^2\)