R
rinnegan_97


giải pt:
[TEX](sin^3( \frac{x}{2})+ \frac{1}{sin^3( \frac{x}{2})})^2 + (cos^3( \frac{x}{2})+ \frac{1}{cos^3( \frac{x}{2})})^2= \frac{81}{4} cos^2(4x)[/TEX]
[TEX](sin^3( \frac{x}{2})+ \frac{1}{sin^3( \frac{x}{2})})^2 + (cos^3( \frac{x}{2})+ \frac{1}{cos^3( \frac{x}{2})})^2= \frac{81}{4} cos^2(4x)[/TEX]
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