In the context of a unit circle, the x and y coordinates of a given point (x, y) correspond to cosine and sine of the angle established by the point and the positive x-axis, respectively.
Specifically, the x-coordinate equals cos(t), and the y-coordinate equals sin(t), where t is the angle.
So, if we have a point (a, b) on the unit circle, it means that it corresponds to an angle t. In such a case, a is the cosine of this angle and b is the sine of the angle.
Therefore, the simplest expression equivalent to cos(t) would match the x-coordinate of the point on the unit circle that corresponds with angle t. So, it is equal to 'a'.
So, looking at the available options a. b b. b/(a+b) c. a d. b/(√a²+b²) e. a/(√a² + b²), the simplest expression that corresponds to cos(t) is 'a', which is option c.
In conclusion, the simplest expression that is equal to cos(t) is 'a', hence option c is the correct answer.