h. The functions of any angle between 180€ and 270 can be expressed as the function of the

acute angle, which is found by subtracting 180 from the given angle. Assuming that angle XAB in

Figure 4-14 can have any value from 180 to 270, you can derive the following formulas for the

functions of any angle in the third quadrant.

(1) Sin of angle XAB:

sin XAB = - sin X1AB =-sin (XAB - 180)

(2) Cos of angle XAB:

cos XAB = -cos X1AB = -cos (XAB - 180)

(3) Tan of angle XAB:

tan XAB = tan X1AB = tan (XAB - 180)

(4) Cot of angle XAB:

cot XAB = cot X1AB = cot (XAB - 180)

(5) Sec of angle XAB:

sec XAB = -sec X1AB = - sec (XAB - 180€)

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