Question

The equation having null set as its solution set is

A) x = cos x
B) x = e^x
C) x = sin x
D) x = tan x

Answer 1

B) x = e^x

Explanation:

The graphs of y = e^x and y = x never intersect, so the solution set will be the empty (null) set for ...

x = e^x

_____

There is one intersection of y=x with cos(x) and with sin(x). There are an infinite number of solutions for x = tan(x).