Section 5.4 – Values of the Trigonometric Functions
We will show how the value of any trigonometric function at an angle of
q
degrees or at
a real number t can be found from its value in the
q
-interval (0°, 90°) or the t-interval (0,
p
/2), respectively.
This technique is sometimes necessary when a calculator is used to find all angles or real
numbers that correspond to a given function value.
The above figure illustrates the reference angle
q
R for a nonquadrantal angle
q
, with
0
°
<
q
< 360
°
or 0 <
q
< 2
p
, in each of the four quadrants.
