Syntax
SEC(number)
| Parameter | Description |
|---|---|
| number | Parameter of the SEC function. |
Examples
Secant of 0
Formula
=SEC(0)
Returns 1. SEC(0) = 1/COS(0) = 1/1 = 1.
Secant of 60 degrees
Formula
=SEC(RADIANS(60))
Returns 2. SEC(60°) = 1/COS(60°) = 1/0.5 = 2.
Verifying identity
Formula
=SEC(A1)^2 - TAN(A1)^2
Returns 1 for any angle in A1. This confirms the identity sec²(x) - tan²(x) = 1.
Common Errors
#DIV/0!
SEC is undefined where COS equals zero: at 90° (π/2), 270° (3π/2), etc. These inputs produce #DIV/0!.
#VALUE!
Non-numeric arguments return #VALUE!.
Tips
1/COS shorthand
SEC(x) = 1/COS(x). Both work, but SEC is cleaner when the formula already uses reciprocal trig functions.
Trig identity
SEC²(x) = 1 + TAN²(x). This identity is useful for simplifying expressions in calculus and physics.
Input is radians
Like all trig functions, SEC expects radians. Use =SEC(RADIANS(degrees)) when working with degree values.
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