(1)

The standard angle is .

Reference angle:

If be an angle in standard position, its reference angle is the acute angle formed by the terminal side of , and the horizontal axis.

if in Third quadrant then .

\ \ The reference angle is

(2)

The standard angle is .

Reference angle:

If be an angle in standard position, its reference angle is the acute angle formed by the terminal side of , and the horizontal axis.

if in Fourth quadrant then .

\ \ The reference angle is

(3)

The standard angle is .

Reference angle:

If be an angle in standard position, its reference angle is the acute angle formed by the terminal side of , and the horizontal axis.

if in First quadrant then .

\ \ The reference angle is