MATHEMATICS - THEORY
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No Inverse Function for
f(x)
= sin x from -∞ to +∞ |
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In this section, the method of finding the derivative
of an inverse trigonometric function is introduced.
It is known that trigonometric functions are not one-to-one function,
and thus they do not have inverse function. However, trigonometric
functions can be converted to one-to-one functions by restricting their
domains. For example, function f(x) = sin x is
not a one-to-one function from -∞ to +∞ and has no inverse function.
This can be seen on the left figure. However, it is a one-to-one
function from -π/2
to +π/2,
and thus f(x) has inverse function in this range. |
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Arcsine Function
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sin x and Its
Inverse Function asin(x)
from -π/2 to +π/2 |
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The inverse function of f(x) = sin x is called
the arcsine function. According to the definition of the inverse function,
the following two equations are obtained and they are reciprocal inverse
functions.
sin-1x = y
sin y = x for
-π/2 ≤ y ≤ +π/2
The cancellation equation y = f(f -1(y)) and x = f -1(f(x))
for arcsine function becomes
sin-1 (sin x) = x for
-π/2 ≤ x ≤ +π/2
sin (sin-1 x) = x for
-1≤ x ≤ +1
The derivative of an arcsine function can be calculated as
where -1< x < +1 |
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Inverse Cosine Function
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The inverse cosine function is denoted by cos-1 or
arccos. Its definition states:
cos-1x = y
cos y = x
are reciprocal inverse
functions where 0 ≤ y ≤ π.
The cancellation equations for inverse cosine function are
cos-1 (cos x) = x for
0 ≤ x ≤ π
cos (cos-1 x) = x for
-1 ≤ x ≤ +1
The derivative of the inverse cosine function is given by
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Inverse Tangent Function
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tan x and Its Inverse
Function atan x
in -π/2 to +π/2 |
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The inverse tangent function is defined as
the inverse function of tangent function and denoted as tan-1 or
atan. Its domain is the interval (-π/2,
+π/2). Its definition states:
tan-1x = y
tan y = x
are reciprocal inverse functions where -π/2 ≤ y ≤ +π/2.
The arctangent function is horizontal asymptotes because when x approaches
+∞, 1/x is extremely close to +π/2 and
when x approaches -∞, 1/x is extremely close to -π/2.
This can be expressed with mathematics equations:
and
The derivative of the inverse arctangent function is given by
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Other Inverse Trigonometric Function
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The definition of csc-1 is given
by
sec-1x = y for
|x| ≥ 1
sec y = x for
y ∈[0, π/2] ∪ [π/2,
0]
The definition of csc-1 states
csc-1x = y for
|x| ≥ 1
csc y = x for
y ∈(0, π/2] ∪ [π,
3π/2]
The definition of cot-1states
cot-1x =& y
cot y = x for
y ∈(0, π) |
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Derivative for Inverse Trigonometric Functions
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Inverse trigonometric functions also have
integration and derivation. Some of the formulas are listed in the
table. |
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