注：如cos2θ=3/9则有：　　cos²θ-sin²θ=3/9所以可得：cos²θ=13/18, sin²θ=7/18sin4次方θ+cos4次方θ=(sin²θ+cos²θ)²-2sin²θcos²θ=1-2x7/18x13/18=53/14...