Final answer:
The differential of y when y = 3 cos(x) at x = 103 is -3sin(103), which corresponds to option a).
Step-by-step explanation:
The differential of y with respect to x, where y is a function of x, is found by taking the derivative of y. Given that y = 3 cos(x), we can use the chain rule to differentiate: dy/dx = -3 sin(x).
Therefore, at x = 103, the differential of y is -3 sin(103). Hence, the correct answer is option a) −3sin(103).