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tieunuhuyenbi207


1) $cos^2x+\dfrac{1}{cos^2x}=2(cosx+\dfrac{1}{cosx}) +1$
2)$sin^2x +\dfrac{1}{sin^2x} +sinx +\dfrac{1}{sinx}=7/4$
2)$sin^2x +\dfrac{1}{sin^2x} +sinx +\dfrac{1}{sinx}=7/4$
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