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chapter3.6r
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à 3.6ïInverse Trigonometric Functions
äïPlease use your built-in calculator to find the inverse
êêsine of the given value.
â
#êêèFind Sinúî(-.2456) in radian measure.
#êêêïSinúî(-.2456)ï≈ï-.2481
éSïSince the trigonometric functions are not one-to-one, their in-
verses are not functions.ïIt is possible, however, to restrict the do-
mains of the trigonometric functions so that the remainder of the curves
are one-to-one.ïThat will allow the inverse trigonometric functions to
exist if only for the small restricted parts of the curves.ïFor exam-
ple, the standard restriction of the domain of the sine curve is the in-
terval, -π/2 ≤ x ≤ π/2.ïThis restricted part is called the principal
part of the sine curve.ïSince this restricted part is one-to-one, the
#inverse, y = Sinúî(x), is a function whose domain is -1 ≤ x ≤ 1 and
whose range is -π/2 ≤ y ≤ π/2.ïA graph of the restricted sine curve and
it's inverse are shown below.
@fig3601.bmp,125,215
#è The Sinúî of a real number "b" (think of b as the "y-leg" of the
triangle in the unit circle in the Key Feature) is defined to be the
arc length subtended by the central angle.ïYour built-in calculator is
#programmed to find the Sinúî of any value of x from -1 to 1.ïAlso, in
#the Key Feature, for a particular angle, you can see that the Sinúî of
the "y-leg" of the triangle in the unit circle is either the central an-
gle in radians or the real number length of the arc subtended by the
central angle. The central angle in radians always equals the subtended
#arc length.ïThe Sinúî of a value of x can also be given in degree mea-
sure.
è You are encouraged to go to your Function Plotter to draw a graph of
#y = Sinúî(x).ïYou will see from the graph that the approximate value of
#Sinúî(-.2456), for example, is -.25.ïThe calculator gives a more accu-
rate value of -.2481.
1êë Use your calculator to find
#êêë Sinúî(.8321) in radian measure.
êêA)ï.1128êêê B)ï.6917
êêC)ï.9829êêê D)ïå of ç
ü
#êêêèSinúî(.8321)ï≈ï.9829
Ç C
2êë Use your calculator to find
#êêë Sinúî(-.6932) in radian measure.
êêA)ï.6132êêê B)ï-.7659
êêC)ï-.8317êêêD)ïå of ç
ü
#êêêèSinúî(-.6932)ï≈ï-.7659
Ç B
3êë Use your calculator to find
#êêê Sinúî(0) in radian measure.
êêA)ï0êêêëB)ï1
êêC)ï-1êêêè D)ïå of ç
ü
#êêêë Sinúî(0)ï=ï0
Ç A
4êë Use your calculator to find
#êêê Sinúî(-2) in radian measure.
êêA)ï-1êêêè B)ïerror
êêC)ï0êêêëD)ïå of ç
ü
#êêêèSinúî(-2)ï=ïerror
#êThe value, -2, is not in the domain of the Sinúî function.
Ç B
äïPlease use your built-in calculator to find the inverse
êêtrigonometric functions of the given value.
âS
#êêêCosúî(-.3821)ï≈ï1.9629 radians
#êêêtanúî(6.381)ï≈è81.09°
#êêêsecúî(2.384)ï≈ï1.1379 radians
#êêêcotúî(-3.145)ï≈ï2.8337 radians
éSïEach of the remaining trigonometric functions is restricted in
a way similar to that of the sine function, although there is no general
agreement on the principal parts for the secant or the cosecant.ïThe
following chart shows the domain and ranges for the remaining inverse
trigonometric functions.
ê FunctionêêDomainêê Range
#è y = Cosúî xêê -1 ≤ x ≤ 1êè 0 ≤ y ≤ π
#è y = Tanúî xêê -▄ ≤ x ≤ ▄êè -π/2 ≤ y ≤ π/2
#è y = Cscúî xêê (-▄,-1] U [1,▄)ë (-π/2,0) U (0,π/2)
#è y = Secúî xêê (-▄,-1] U [1,▄)ë (0,π/2) U (π/2,π)
#è y = Cotúî xêê -▄ < x < ▄êè 0 < y < π
è Graphs of ç inverse trigonometric functions can be drawn on your
#Function Plotter.ïYou can use your calculator to find the Cosúî of any
#value of x from -1 to 1, and the Tanúî of any value of x on the real
number line.ïThe calculator is not programmed for the inverse cotan-
gent, inverse secant, or inverse cosecant. You can, however, use the re-
ciprocal relationships and the following table showing the sequence of
keystrokes necessary for ç cases.
ê Inverse FunctionëSequence of Keystrokes
#ê y = Cscúî xêèx, 1/x, Sinúî
#ê y = Secúî xêèx, 1/x, Cosúî
#êêêê ┌
#ê y = Cotúî xêè│ x, 1/x, Tanúî,èif x is positive
#êêêê │ x, 1/x, Tanúî, +, π, =,ïif x is negative
#êêêê └
#è To find Cotúî(-3.145), for example, you would use the following key-
#stroke sequence:ï-3.145, 1/x, Tanúî, +, π, =.ïThus, Cotúî(-3.145) is
approximately 2.8337 radians.
5êë Use your calculator to find
#êêë Cosúî(-.1423) in radian measure.
êêA)ï1.7136 radiansêèB)ï2.3146 radians
êêC)ï.9732 radiansêè D)ïå of ç
ü
#êêêèCosúî(-.1423)ï≈ï1.7136 radians
Ç A
6êë Use your calculator to find
#êêë Tanúî(-3.468) in radian measure.
êêA)ï2.184 radiansêè B)ï-1.2865 radians
êêC)ï-1.2901 radiansêïD)ïå of ç
ü
#êêêèTanúî(-3.468)ï≈ï-1.2901 radians
Ç C
7êë Use your calculator to find
#êêë Secúî(2.483) in degree measure.
êêA)ï38.2°êêëB)ï66.25°
êêC)ï45.7°êêëD)ïå of ç
ü
#êêêèSecúî(2.483)ï≈ï66.25°
Ç B
8êë Use your calculator to find
#êêë Cscúî(-7.834) in degree measure.
êêA)ï-7.33°êêè B)ï22.4°
êêC)ï-36.8°êêè D)ïå of ç
ü
#êêêèCscúî(-7.834)ï≈ï-7.33°
Ç A
9êë Use your calculator to find
#êêë Cotúî(6.384) in degree measure.
êêA)ï63.4°êêëB)ï8.9°
êêC)ï159.1°êêè D)ïå of ç
ü
#êêêèCotúî(6.384)ï≈ï8.9°
Ç B
10êëUse your calculator to find
#êêë Cotúî(-6.384) in degree measure.
êêA)ï6.39°êêëB)ï-7.8°
êêC)ï171.1°êêè D)ïå of ç
ü
#êêêêCotúî(-6.384)
è To find this angle you should use the following keystroke sequence.
#êêêè-6.384, 1/x, tanúî, +, 180°,=
This sequence of keystrokes gives 171.1°.
Ç C