Question

I have tried writing this in Android and I get NAN as the result. This is my current code can someone verify this, and if it is not correct, offer me the correct equation.

 Math.acos((((a*a)+(c*c))-(b*b))/(2*b*c));

Answer 1

Math.acos((a*a+c*c-b*b)/(2.0*b*c)) 

2.0 is used to convert it into double, you could also use
Math.acos((a*a+c*c-b*b)/(2d*b*c)) instead where d in 2d means treat int 2 as double type