How do you simplify Cotangent(Arcsin)?

1 Answer
Jun 15, 2015

#cot(arcsinx) = (cos(arcsinx))/(sin(arcsinx))#

#= (cos(arcsinx))/x#

Normally, here would be enough for a high school Pre-Calculus problem. But, let's try something creative.

#d/(dx)[cos(arcsinx)] = -sin(arcsinx) * 1/(sqrt(1-x^2)) = -x/sqrt(1-x^2)#

Let:
#u = 1-x^2#
#du = -2xdx#

#int (-x)/(sqrt(1-x^2))dx = 1/2int (-2x)/(sqrt(1-x^2))dx#

#= 1/2int 1/(sqrt(u))du#

#= 1/2int u^(-1/2)du#

#= 1/2*[2sqrtu] = sqrtu = sqrt(1-x^2)#

There, now we have a representation for #cos(arcsinx)#.

#int{d/(dx)[cos(arcsinx)]}dx = cos(arcsinx)#

We haven't changed the domain, since the domain of #sinx# and #cosx# are larger than that of #arcsinx#. Thus, #arcsinx# decides the domain restrictions on the left and right boundaries. Remember the #x# in the denominator adds a vertical asymptote at #x = 0#.

#=> (cos(arcsinx))/x = sqrt(1-x^2)/x#

#AA x in [-1, 0) uu (0, 1]#
(For all #x# in the domain of #-1 <= x < 0# and #0 < x <= 1#)