I have the following formula in a form "this.getField("Thickness")/Math.cos(this.getField("TransducerAngle")). I am trying to calculate T/cosine(X degrees) where T is the Thickness and X is the Angle. this is my best effort at it but it is not work

You will need to correctly convert the value in degrees to radians to use the Math.cos method. Also, check the JavaScript console (Ctrl + J) to see if any error are reported. Finally, since the denominator could conceivably be zero (or very close), you should not perform the division if it is and set the field value to something else, perhaps blank.