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à 1.4ïTrigonometric Functions of any Angle
äïPlease find the trigonometric functions of the given an-
êêgles.
âS
êêêësin 186°è≈è-.1045
êêêëcos 235°è≈è-.5736
êêêëtan -47°è≈è-1.072
êêêè sec 12π/5è≈è3.2361
éSïIn the next section on solving oblique triangles, it will be
necessary to find the sin and cos of obtuse angles (0° < Θ < 180°) in
order to solve the triangles.ïAlthough this involves only angles in
the first and second quadrants, it is convenient at this point to
define trigonometric ratios of angles in all quadrants.ïYou will
see that the primary difference in quadrants II, III, and IV is
@fig1401.bmp,10,170
that the trigonometric ratios are ratios of the coordinates of the point
"P" and the distance "r" instead of ratios of positive sides of trian-
gles.êêêèRatios for angles in Quadrant I
êêêësin Θï=ïy/rêè csc Θï=ïr/y
êêêëcos Θï=ïx/rêè sec Θï=ïr/x
êêêëtan Θï=ïy/xêè cot Θï=ïx/y
Ratios for angles in Quadrant II
@fig1402.bmp,390,170
sin Θï=ïy/rêè csc Θï=ïr/y
cos Θï=ï-x/rêèsec Θï=ïr/-x
tan Θï=ïy/-xêècot Θï=ï-x/y
êêêê Ratios for angles in Quadrant III
@fig1403.bmp,10,170
êêêësin Θï=ï-y/rêècsc Θï=ïr/-y
êêêëcos Θï=ï-x/rêèsec Θï=ïr/-x
êêêëtan Θï=ï-y/-xêïcot Θï=ï-x/-y
êêêë(more...)
Ratios for angles in Quadrant IV
@fig1404.bmp,390,170
sin Θï=ï-y/rêècsc Θï=ïr/-y
cos Θï=ïx/rêè sec Θï=ïr/x
tan Θï=ï-y/xêècot Θï=ïx/-y
The quadrantal angles 0°, 90°, 180°, 270°, and
êë360° are shown below.
ësinècosètanècscèsecècot
#ï0°è0ë1ë0ë▄ë1ë▄
# 90°è1ë0ë▄ë1ë▄ë0
#180°è0è -1ë0ë▄è -1ë▄
#270°ï-1ë0ë▄è -1ë▄ë0
#360°è0ë1ë0ë▄ë1ë▄
You should study the "Key Feature" in this program
to more clearly understand ç definitions. It is
absolutely wonderful that the calculator takes care
of signs, quadrants, and quadrantal angles internally.
1êêêëFind the sin 30°.
êêêêA)ï√3êêïB)ï√3/2
êêêêC)ï1/2êê D)ïå of ç
@fig1405.bmp,25,118
ü
êêêêêïyê1
#êêêïsin 30°è=è─è=è─
êêêêêïrê2
Ç C
2êêêëFind the cos 120°.
êêêêA)ï-1/2êêB)ï-2
êêêêC)ï√3/2êêD)ïå of ç
@fig1406.bmp,15,118
ü
êêêêêï-xë -1
#êêêïcos 120°è=è─è=è─
êêêêêèrê2
Ç A
3êêêëFind the tan 135°.
êêêêA)ï√2êêïB)ï1/√2
êêêêC)ï-1êêïD)ïå of ç
@fig1407.bmp,25,118
ü
êêêêêèyê1
#êêêïtan 135°è=è─è=è─è=è-1
êêêêêï-xë -1
Ç C
4êêêëFind the sec 210°.
êêêêA)ï-2êêïB)ï√3
êêêêC)ï2/-√3êë D)ïå of ç
@fig1408.bmp,25,118
ü
êêêêêèrê 2
#êêêïsec 210°è=è─è=è──.
êêêêêï-xë -√3
Ç C
5êêêëFind the cot 225°.
êêêêA)ï-1êêïB)ï1
êêêêC)ï√2êêïD)ïå of ç
@fig1409.bmp,25,118
ü
êêêêêï-xë -1
#êêêïcot 225°è=è─è=è─è=è1
êêêêêï-yë -1
Ç B
6êêêëFind the csc 11π/6.
êêêêA)ï-2êêïB)ï√3/2
êêêêC)ï-1/2êêD)ïå of ç
@fig1410.bmp,25,118
ü
êêêêêè rê2
#êêêïcsc 11π/6è=è─è=è─è=è-2
êêêêêè-yë -1
Ç A
7
êêïUse your calculator to find the cos 756°.
êêïA)ï-.1405êêêB)ï.6231
êêïC)ï.8090êêê D)ïå of ç
ü
êêêècos 756°è≈è.8090
Ç C
8
êêïUse your calculator to find the tan -193.7°.
êêïA)ï-.2438êêêB)ï21.426
êêïC)ï.7237êêê D)ïå of ç
ü
êêêètan -193.7°è≈è-.2438
Ç A
9
êêïUse your calculator to find the sec -π/4.
êêïA)ï-.7071êêêB)ï1.414
êêïC)ï√2/2êêêïD)ïå of ç
ü
êêêèsec -π/4è≈è1.414
Ç B
äïPlease find the inverse trigonometric function of the
êêgiven ratio.
âS
#êë The sinúî 1/2, with Θ in quadrant II, is 150°.
#êë The cosúî √3/2, with Θ in quadrant IV, is 330°.
#êë The tanúî 1, with Θ in quadrant III, is 225°.
éSïIn Section 1.2, we looked at inverse trigonometric functions of
ratios of only acute angles or quadrant I angles.ïIn this section, we
are expanding this to inverse trigonometric functions of ratios of an-
gles in any quadrant.
#è In the example, you are asked to find the sinúî 1/2.ïThe sin of an
angle involves "y" and "r", since r is always positive, the sin of an
angle is positive whenever "y" is positive.ïThis occurs in quadrants
I and II.ïSince the ratio "1/2" comes from the 30°-60° triangle, the
first quadrant angle is 30° and the second quadrant angle is 150°.
Thus, there are two answers.ïHowever, since the problem requested only
the second quadrant angle, the correct answer is 150°.
#è To find the cosúî (√3/2), with Θ in quadrant IV, we can reason in a
similar way.ïThe cos is positive whenever "x" is positive, and that
occurs in quadrants I and IV.ïSince the ratio "√3/2" involves the 30°-
60° triangle, and we are looking for a fourth quadrant angle, Θ must
be 330°.
#è To find the tanúî 1, with Θ in quadrant III, we determine that the
tan is positive in quadrants I and III.ïThe ratio "1" comes from the
45°-45° triangle.ïThus, the third quadrant angle is 225°.
è When you use your calculator, you get only the reference angle.ïYou
have to use this reference angle to get an angle in the correct qua-
#drant.ïFor example, when you use your calculator to find the sinúî 1/2,
with Θ in quadrant II, the calcuator gives you 30°.ïThis reference an-
gle subtracted from 180° gives the second quadrant angle, 150°.
#è Similarly, when you use your calculator to find the cosúî (√3/2),
with Θ in quadrant IV, your calculator gives you 30°.ïThis reference
angle subtracted from 360° gives the fourth quadrant angle, 330°.ïAlso,
#when you use your calculator to find the tan úî 1, you get 45°.ïThis
reference angle is added to 180° to get the third quadrant angle, 225°.
10
#êêFind the sinúî (1/√2), with Θ in quadrant II.
êêA)ï45°êêêê B)ï225°
êêC)ï135°êêêêD)ïå of ç
ü
#è Using the calculator, sinúî (1/√2)è=è45°.ïThis reference
è angle is subtracted from 180° to get the second quadrant
è angle, 135°.
Ç C
11
#êêFind the cosúî .4321, with Θ in quadrant IV.
êêA)ï295.6°êêêêB)ï-236.8°
êêC)ï157.3°êêêêD)ïå of ç
ü
#è Using the calculator, cosúî .4321è≈è64.4°.ïThis reference
è angle is subtracted from 360° to get the fourth quadrant
è angle, 295.6°.
Ç A
12
#êêFind the tanúî (-2.432), with Θ in quadrant II.
êêA)ï226°êêêêïB)ï112.35°
êêC)ï159.1°êêêêD)ïå of ç
ü
#è Using the calculator, tanúî (-2.432)è≈è-67.65°.ïThis reference
è angle is added to 180° to get the second quadrant angle, 112.35°.
Ç B