<span>A. y=secx
This problem deals with the various trig functions and is looking for those points where they are undefined. Since the only math operations involved is division, that will happen with the associated trig function attempts to divide by zero. So let's look at the functions that are a composite of sin and cos.
sin and cos are defined for all real numbers and range in value from -1 to 1.
sin is zero for all integral multiples of pi, and cos is zero for all integral multiples of pi plus pi over 2. So the functions that are undefined will be those that divide by cos.
tan = sin/cos, which will be undefined for x = π/2 ±nπ
cot = cos/sin, which will be undefined for x = ±nπ
sec = 1/cos, which will be undefined for x = π/2 ±nπ
csc = 1/sin, which will be undefined for x = ±nπ
Now let's look at the options and pick the correct one.
A. y=secx
* There's a division by cos, so this is the correct choice.
B. y=cosx
* cos is defined over the entire domain, so this is a bad choice.
C. y=1/sinx
* The division is by sin, not cos. So this is a bad choice.
D. y=cotx,
* The division is by sin, not cos. So this is a bad choice.</span>
