What is Secant
Let a right-angled triangle ABC with an acute angle α be given, then the cosine of angle α will be the ratio of the hypotenuse to the adjacent leg
sec α = AC/AB .
Also, to determine the secant of an angle, you can use a circle built in a Cartesian coordinate system, radius R and center at the origin O.
On the circle, mark the point P with coordinates (1; 0), now turn the ray OP by some angle α.
Counterclockwise direction is considered positive, clockwise direction is negative.
The secant of angle α is the ratio of the radius of the circle to the abscissa of point XP
sec α = R/XP, if the circle is unit (circle radius = 1), the formula will take the form sec α = 1/XP
and since the cosine of the angle is equal to the abscissa of point XP, we can write sec α = 1/cos α .