Wednesday, November 13, 2013

Prove the identity arc sin squareroot(1-x^2)+ arc cos x=pi, if -1=

Since the result of the given sum is a constant, then the
value of th derivative of the sum must be zero.


We'll
assign a function to the given expression:


f(x) = arcsin
sqrt(1-x^2) + arccos x


We'll differentiate with respect to
x:


f'(x) = [sqrt(1-x^2)]'/sqrt(1 - 1 + x^2) - 1/sqrt(1 -
x^2)


f'(x) = -2x/2*|x|*sqrt(1-x^2) - 1/sqrt(1 -
x^2)


Since x is in the interval [-1 , 0] => |x| =
-x


f'(x) = -2x/-2x*sqrt(1-x^2) - 1/sqrt(1 -
x^2)


f'(x) = 1/sqrt(1 - x^2) - 1/sqrt(1 -
x^2)


f'(x) = 0


Since the 1st
derivative of f()x is cancelling out, then the function f(x) is a
constant.


Now, we'll check if the constant is
pi.


Let x = -1. We'll compute the value of f(x) for x
=-1.


f(-1) = arcsin sqrt(1 - 1) +
arccos(-1)


f(-1) = arcsin 0 +
arccos(-1)


f(-1) = 0 +
pi


f(-1) = pi


We'll replace x
by 0 and we'll get:


f(0) = arcsin sqrt(1 - 0) +
arccos(0)


f(0) = arcsin 1 + arccos
0


f(0) = pi/2 + pi/2


f(0) =
2pi/2


f(0) =
pi


The identity arcsin sqrt(1-x^2) + arccos x
= pi is verified for any value of x, over the range [-1 ,
0].

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