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4cos²x - sin²x = -1
4cos²x - sin²x = -(sin²x + cos²x)
4cos²x + cos²x - sin²x + sin²x = 0
5cos²x = 0 /:5
cos²x = 0 /√
cosx = 0
b)
2 + sin²x = 4 - cos²x + cosx
2 + 1 - cos²x = 4 - cos²x + cosx
3-4 = cosx
cosx = -1