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It is proved that the value of 2 + cosx + SiNx * cosx is always greater than 0
2+cosx+sinx*cosx
=2+cosx+1/2sin2x
Because cosx > = - 1, sin2x > = - 1
SO 2 + cosx + SiNx * cosx > = 1 / 2 > 0
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