How do you solve #2 cos-1 x = pi#?

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Answer 1 · 2018-02-24T18:48:12

#color(blue)(x=0)#

I'm reading this as #2cos^-1(x)=pi#

#2cos^-1(x)=pi#

Divide both sides by 2:

#cos^-1(x)=pi/2#

Take the cosine of both sides: *

#cos(cos^-1(x))=cos(pi/2)#

#x=cos(pi/2)#

#cos(pi/2)=0#

Hence:

#color(blue)(x=0)#

*
If #y=cos(x)#

Then:

#x=cos^-1(y)#

#cos(cos^-1(y))=cos(x)=y#