Hey guys this is the question:
$$(\cos\theta - \sin\theta)^2 + (\cos\theta + \sin\theta)^2 = 2$$
I did this before but I forgot how I did it.. I tried to do this but don't know how to continue.. btw I can only use identity formulas, so please don't answer with other formulas I don't know about...
$$\cos^2\theta - 2\cos\theta\sin\theta + \sin^2\theta + 1 = 2$$
$$1 - 2\cos\theta\sin\theta = 2$$
then idk.. please help!