Which equation should be used to graph y=sec^-1 (x) on a calculator?

y=1/sec (x)

y=1/cos^-1 (x)

y=sec (1/x)

y=cos^-1 (1/x)

Arcsecant or arcsec or sec⁻¹ is an inverse trigonometric function. And many calculators don't have a key for them because they can be calculated with basic trigonometric functions like so:

sec⁻¹ (x) = cos⁻¹ (1/x).

So the correct answer is the fourth one: y=cos⁻¹ (1/x).