Question

It is given that cos^2 y + cos y = p . Determine the value of p if sin y = sin y . Cos y

Answer 1

Are you using the . in siny.cosy as a multiplication sign?
If so, then
siny = sinycosy
cosy = 1

and cos^2 y + cosy = p
1+1 = p

p = 2

Am I missing something here??
Looks too easy, did you have a typo?

Answer 2

of course , if siny = 0, then we have cosy = 1 or -1.

You can try those for other solutions.