Answer:
If the equation is exactly the one you posted then the unique answer is:
[tex]y = 0[/tex]
or what is the same:
[tex]y=0K[/tex]
Explanation:
If your equation is exactly the one you posted then it has only one solution: y = 0
Because the range of [tex]y=\cos^{-1}(x)[/tex] is the interval [tex][0, \pi][/tex]
The meaning of [tex]\cos^{-1}(1)[/tex] is to find the angle whose cosine is 1.
In the range of the function arccosine the only angle whose cosine is 1 is the angle 0.
But if your equation was the following one:
[tex]\cos(y)=1[/tex]
Then in that case we would have infinite solutions since it will be the set:
[tex]y=\cos^{-1}(1)+2K\pi[/tex] where K is an integer, since the period of cosine is [tex]2\pi[/tex]
So, in such a case the solution set would be:
[tex]y=0+2K\pi=2K\pi[/tex]
But for the equation you posted, the unique solution is: y = 0 or what is the same y = 0K
