- 26 Tháng sáu 2015
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- Đắk Lắk
- THPT chuyên Nguyễn Du


Cho [tex]\large 2 \cos(\alpha +\beta )=\cos\alpha \cos(\pi +\beta )[/tex]. Tính [tex]\large A=\dfrac{1}{2\sin^2\alpha +3\cos^2\alpha}+\dfrac{1}{2\sin^2\beta+3\cos^2\beta}[/tex]
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