1. The problem statement, all variables and given/known data My trig is really rusty and I've been trying to figure out why the answer is what it is: Find all solutions of the following equation: sin2 x + cos x - 1. 2. Relevant equations Just the identity: sin2 θ + cos2 θ = 1 3. The attempt at a solution The sin2 x is in the way, so I substitute 1 - cos2 x in it's place to get: (1 - cos2 x + cos x - 1 = 0 The ones are removed and cos x is common, so: cos x(-cos x + 1) = 0 This means that: cos x = 0 or cos x = -1 From the unit circle, we get: cos x = ∏/2 or cos = ∏ Here is where I get confused: I know we need to make this true for all intervals so: cos x = 0 whenever x = ± ∏/2 + 2k∏ or, cos x = -1 whenever x = ± ∏ + 2k∏ for any integer k. That's my final answer. According to my textbook, It's wrong, but I have no idea why. The textbook gives the final answer as: cos x = 0 whenever x = ∏/2 + 2k∏ or, cos x = -1 whenever x = ∏ + 2k∏ for any integer k. Is it wrong that x = ± ∏/2 or x = ±∏?