What is the exact value of sec^-1 (sqrt2) and csc^-1 (2)sec1(2)andcsc1(2)?

1 Answer
Mar 28, 2018

sec^-1(sqrt2)=pi/4sec1(2)=π4
csc^-1(2)=pi/6csc1(2)=π6

Explanation:

Note:
color(red)((1)sec^-1x=cos^-1(1/x)(1)sec1x=cos1(1x)

color(red)((2)csc^-1x=sin^-1(1/x)(2)csc1x=sin1(1x)

color(red)((3)cos^-1(costheta))=color(red)(theta,where,theta in [0,pi](3)cos1(cosθ)=θ,where,θ[0,π]

color(red)((4)sin^-1(sintheta))=color(red)(theta,where,theta in [-pi/2,pi/2](4)sin1(sinθ)=θ,where,θ[π2,π2]

Here,

sec^-1(sqrt2)=cos^-1(1/sqrt2)...toApply (1)

sec^-1(sqrt2)=cos^-1(cos(pi/4))

sec^-1(sqrt2)=pi/4in[0,pi].............toApply(3)

Now,

csc^-1(2)=sin^-1(1/2).....toApply(2)

csc^-1(2)=sin^-1(sin(pi/6))

csc^-1(2)=pi/6in[-pi/2,pi/2]..........toApply(4)