You need to use the fact that the tangent function is a
rational function such that: `tan x = sin x/cos x`
Using
the following formulas `sin (x+y) = sin x*cos y + sin y*cos x ` and `cos(x+y) = cos
x*cos y - sin x* sin y` yields:
`tan
(cos^-1(4/5)+sin^-1(1)) = (sin (cos^-1(4/5)+sin^-1(1)))/(cos
(cos^-1(4/5)+sin^-1(1)))`
`tan (cos^-1(4/5)+sin^-1(1)) =
(sin (cos^-1(4/5))*cos(sin^-1(1)) +
sin(sin^-1(1))*cos(cos^-1(4/5)))/(cos(cos^-1(4/5))*cos(sin^-1(1)) -
sin(sin^-1(1))*sin(cos^-1(4/5)))`
Use `sin(sin^-1 a) = a`
and `sin(cos ^-1 a) = sqrt(1 - a^2),`
` cos(cos^-1 a) = a
and cos(sin ^-1 a) = sqrt(1 - a^2).`
`tan
(cos^-1(4/5)+sin^-1(1)) = (sqrt((1 - 16/25)(1 - 1)) + 1*(4/5))/((4/5)*sqrt(1-1) -
1*sqrt(1 - 16/25))`
`tan (cos^-1(4/5)+sin^-1(1)) = (0 +
4/5)/(0 - sqrt(9/25))`
`tan (cos^-1(4/5)+sin^-1(1)) =
(4/5)/(-3/5)`
`tan (cos^-1(4/5)+sin^-1(1)) =
-4/3`
Hence, evaluating the tangent of the
sum of inverse trigonometric functions yields`tan (cos^-1(4/5)+sin^-1(1)) = -4/3.`
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